https://www.cnet.com/news/facebook-messenger-may-be-getting-an-unsend-feature-soon/

"Facebook Messenger is finally working on 'Unsend Message' in the app for everyone," she tweeted. 

Currently, when users delete something they sent on Messenger, it disappears only from their own inbox. The recipient can still see the message. The Unsend feature would let users retract their messages from both inboxes.