https://www.theverge.com/2019/2/5/18211255/facebook-messenger-unsend-delete-feature-sent-mark-zuckerberg

Facebook has come out with a feature that lets you delete messages from a conversation after you’ve sent them, as previously spotted in leaks. So in case you send the wrong message to the wrong person or make an egregious typo, you’ll be able to remove it in Messenger now.

It works when you tap on the message you want to delete within 10 minutes of sending it. Two options will appear: Remove for Everyone and Remove for You. Selecting Remove for Everyone replaces your message with text that the message has been removed by you.