Starting from iOS 16 Software Version, you can EDIT or UNSEND an iMessage after it is sent.

Edit iMessage

In a iMessage Conversation to Edit an iMessage, touch and hold a message untill the menu appears

Tap on Edit

You can make edit or even re-edit the entire message

Once edit is done, just tap on the check-mark at the right of the message

You can edit an message within 15 minutes after sending the original message

And the same message can be edited upto five times

You and recipient can view the edit history, if you both using iOS 16

Just tap edited below the message, to view what changes were made

Tap hide edits to return to the conversation

UNSEND an iMessage

Need to unsend an iMessage, you can make a message disappear within 2 minutes of sending it, as long as the receipient is also using iOS 16, the message will disappear for them too.

Just touch and hold the message untill the menu appears

And tap Undo Send