Deleting messages on Messenger is something we do almost without thinking. Whether it's to free up space or because we believe we won't need them, deleting them seems like the best option. Do you want to recover deleted messages? In the United States, people use little-known tricks to do so.
Recover deleted messages from your computer
If you usually use Facebook Messenger on your PC, you have an advantage. Facebook keeps many of your archived conversations, and you can easily access them. You just need to log in to Facebook from your browser, go to Messenger, and click on "See all in Messenger." Then, look for the gear icon to open settings and select "Archived conversations."
There you'll see all the chats you archived, which aren't the same as deleted ones, but we sometimes confuse them. To "recover" an archived chat, simply send a message in that conversation and it'll reappear in your main list.

Additionally, Facebook lets you download a copy of all your messages. In Settings, go to "Your Facebook information" and select "Download your information." Choose only messages and download the file to have a secure backup.
Recover deleted messages on your Android phone
On Android, deleted messages don't completely disappear, since they're temporarily stored in the device's memory.
To recover them, open internal storage or the SD card and look for the Facebook folder. Inside, you'll find a folder called "cache" where there's a file named "FB.TEMP." Your most recent messages, including deleted ones, are stored there.
This method is very useful for recovering deleted conversations without needing external apps. Be careful, it only works if you haven't deleted the cache or formatted the phone.
Recover deleted messages on iPhone with external help
iPhone users have a bit more work, since iOS doesn't let you easily access temporary files.

The solution is to use external programs like FonePaw. Connect your iPhone to the computer, run the program, and let it scan the device for deleted Messenger data.
When it's done, you'll be able to see the deleted conversations and choose which ones you want to restore. It's a simple process, although it requires you to have your iPhone on hand and a PC. Keep in mind that if you've already formatted your phone or deleted data a long time ago, this option may not work.
What if you don't have a copy or file?
If you haven't archived conversations or downloaded your data, recovery becomes more complicated. Facebook only keeps deleted messages for up to 90 days, after that time there's no way to recover them.
That's why the most recommended thing is to make periodic backups. Even if it's a bit tedious, you'll avoid losing important messages in the future.