The ability to edit your DMs lets you fix a typo or change things around if your message doesn’t quite sound right. To edit a message, you need to press and hold it, and then choose “edit” from the drop-down menu. Once you edit a message, the purple text bubble will have an “Edited” label on top of it to notify the other person that the message has been changed. The feature works similar to Apple’s edit feature for iMessage, which launched nearly two years ago.
https://techcrunch.com/2024/03/04/instagram-now-lets-you-edit-dms-up-to-15-mins-after-sending-them/