You can edit a message you’ve already sent by hovering over it and clicking the “edit” icon, which will create a new “fork” in the conversation. You can toggle between forks as needed too.
I dont think you can jump back though, right? If you change a previous prompt, you’re just resetting to that point and creating a new thread at the expense of the old one? I use this feature but have coke to the conclusion this is how it works. Have you seen differently?
Once you've changed a prompt, a pair of arrows show up to the left of the prompt allowing you to toggle between the new and old prompts!