How can I delete Facebook messages I've sent to other Facebook users from their inbox?
I have had a conversation with my friend but now I want to delete my messages from that conversation. Can I have them deleted from my friend's inbox?
Since February 2019, New Messenger Feature Gives You Ability to Remove Messages for Everyone.
Simply tap on the message you want to remove and select the option to “Remove for Everyone”. The removed message will be replaced by text alerting everyone in the conversation the message was removed. You will have up to 10 minutes to remove a message after it is sent.
No, sent messages can't be unsent or removed from the recipient's inbox. Depending on the persons's notification settings, they may also receive your message as an email notification.
Source: Facebook Help Centre
Using "delete" in the messenger deletes the message in your version of the thread but not the recipient's. So deleting a message or conversation from your inbox won't delete it from your friend's inbox. It isn't possible to delete sent or received messages from a friend's inbox.
However there is some workaround is to mark the message as Spam or Abuse (in Actions), then delete it from your messages, and disable/deactivate your account (and re-activate it after few hours), so both people won't see it.
See also:
Once you've sent a message to someone else, you can't delete it from their inbox. Only they can.
You can delete a message by tapping and holding the message and selecting "Remove". (In the web app, hover above the message, then select "..." and "Remove".) If you do this within ten minutes of sending the message, you then have a choice of wether to remove the message only on your side or also for the recipient.
If you chose to "Remove for Everyone" they will see a placeholder where the message used to be, informing them that the message has been deleted.
After more than 10 minutes have passed after sending, you can only remove the message for yourself.