Steps to Retrieve an Unsent Message on Messenger
If you want to retrieve an unsent message on Messenger, follow below given steps:
First of all, Open the Messenger app on your phone.
After that, Scroll through your conversation list until you find the conversation with the unsent message and Tap on it.
Tap on "Edit" which is present at the top-right corner of the screen.
Read more here:- https://worldzo.net/how-to-see-unsent-messages-on-messenger/