Have you accidentally deleted some important threads from WhatsApp, tried to recover them using some commercially available mobile file recovery software but had no luck? Sorry, but these kinds of solutions work only with photos, videos and few other types of files, not with WhatsApp messages.
If you want to recover deleted whatsapp messages, the only solution you have available to you is to reinstall the application and follow the standard procedure for restoring the last backup made by the application.
As you probably already know, WhatsApp automatically generates backups of all chats. It does this on a daily, weekly, or monthly basis (depending on your preference) and by using one of these backups you can restore all those conversations that now seem lost forever. Of course, restoring WhatsApp to a previous state will cause you to lose all messages received or sent after the backup date... but at this point I guess the other messages have a higher priority, right? So let's put the chitchat to rest and see right now how to restore all the chats you deleted by mistake.
Recover deleted WhatsApp messages from Android
The Android version of WhatsApp saves chat backups both locally, i.e., on your smartphone's storage, and online on Google Drive. The recovery procedure is the same in both cases, all you need to do is remove WhatsApp from your smartphone (by holding down its icon and dragging it to the trash or by going to Settings > App > WhatsApp), download it again from the Play Store and follow the initial setup procedure of the application.
After performing number verification, the app will automatically detect the presence of a backup and ask you if you want to restore it. At that point, all you have to do is click on the Restore button and all conversations will be restored to the state they were in on the backup date (so accidentally deleted messages will be restored automatically).
If you do not know when the last backup was generated automatically by WhatsApp, open the application on your smartphone, click on the (...) button at the top right and select Settings from the menu that appears. On the screen that opens, select Chats > Chat backups and check the dates listed under Last backup. There should be both the date of the last backup made locally and the date of the last backup saved online on Google Drive.
Now, if the last backup made on Google Drive was made after the date you deleted the messages you now want to restore, uninstall the app from your phone, reinstall it and choose to restore the backup from Google Drive: all the messages of your interest will be restored automatically (except those received after the backup date). If the date of the last backup on Google Drive is after the deletion of the messages you're interested in, you have to go to "plan B", i.e. restore local backups.
Using the backups saved locally, you can restore the status of the application even to a date before the last automatic backup. All you need to do is go into the folder where WhatsApp stores its backup files, locate the one for the date you want to restore the status of your conversations, and rename it so that WhatsApp will consider it the most recent backup to be restored.
To be more precise, what you have to do is install a file manager such as ES File Manager and use it to get into the HomeWhatsAppDatabases folder of the smartphone or sdcardWhatsAppDatabases if you use a microSD card for memory expansion: there you will find a set of files named msgstore-[data].1.db.crypt12 where instead of [date] is the date on which the backup was generated.
If you do not know how to get to the location I just gave you, click on the hamburger icon at the top left of the ES File Manager home screen, select the home or SD card icon from the left sidebar, and go first to the WhatsApp folder and then to the Databases folder.
Then, locate the backup file you want to use in WhatsApp and rename it to msgstore.db.crypt12. If a file with the same name already exists in the folder (it should be the most recent backup generated by the application), delete or rename it in another way. To rename or delete a file with ES File Manager, just keep your finger pressed on its icon and click on the appropriate button that appears at the bottom.
When you are done, you can proceed to remove WhatsApp from your smartphone. If after uninstalling the application from your phone, you get a message from ES File Explorer asking you if you want to delete the remaining WhatsApp Messenger files from your smartphone, decline, or it will also delete the backup that you need to restore.
Now, before reinstalling WhatsApp and proceeding to restore the chats, remove the association between Google Drive and WhatsApp. This way, the application will look for backups directly on your phone's storage and will not attempt to restore chats from the cloud. To do this, go to Google Settings (the gear icon on the screen with the list of apps installed on your phone), select Connected Apps from the screen that opens, and click on the WhatsApp icon and then the Disconnect button. Alternatively, go here and delete WhatsApp from the apps associated with your Google Account.
That's it! Now, open the Play Store, reinstall WhatsApp Messenger, follow the initial setup of the app, and accept the backup you renamed earlier. If everything goes well, you will be able to roll back WhatsApp to the date you wanted and restore the messages you accidentally deleted.
Recovering Deleted WhatsApp Messages from iPhone
On iPhone, you can only restore WhatsApp backups through iCloud, Apple's cloud storage service, so you cannot choose the date to restore the status of your conversations, and you can only restore the most recent backup made by the application. To check the date of your last WhatsApp backup, open the application, select the Settings tab at the bottom right, and navigate to Chats > Chat Backup.
The backup procedure is identical to what we have just seen for Android devices: you must uninstall the application from your phone (by holding your finger on its icon and pressing the "x" that appears in the upper left corner) and reinstall it through the App Store. Then you have to follow the initial configuration procedure of the app and accept the restore of the backup, which will be automatically detected thanks to iCloud.
In the unfortunate event that the iCloud backup is later than the date you deleted the messages you want to restore, you can completely reset the iPhone and restore it via an iTunes or iCloud backup. This is a fairly drastic operation with an uncertain outcome, but it is the only hope for recovering your lost WhatsApp conversations.
To make sure that everything goes smoothly, make sure that your iTunes/iCloud backup is older than the date you deleted your recovered WhatsApp messages (but not too old, otherwise you may lose a lot of recent chats). If you do not know how to restore an iPhone using iTunes or iCloud backups, please read my guide on how to make iPhone backups, where everything is explained.
Recovering deleted WhatsApp messages from Windows Phone
Windows Phone also allows you to restore WhatsApp messages from previous backups, but it does not yet support cloud services (messages are saved locally on the phone's memory or microSD). If you have a phone equipped with Microsoft's operating system and want to check the date of the last backup, start the application, click on the (...) button at the bottom right and select Settings from the menu that appears. On the screen that opens, select the Chat item and check the date indicated under the Backup heading.
If the date of the backup is before the day you deleted the messages you want to restore, uninstall WhatsApp from your smartphone (by holding your finger on its icon and selecting Remove from the menu that appears) and download the application again from the Windows Phone Store.
Once WhatsApp is installed, start it, follow the WhatsApp setup wizard, and after verifying your number, accept to restore the backup of your messages by clicking on the Restore button.