I merged a ticket into the wrong ticket. Is there a way to undo this?
Unfortunately, you can't remove the merge comments that were added to both tickets. You can reopen the merged ticket (find it in "Tickets" sections of the left navigation). Also, I would advise you to clarify the case for a requester if he was notified about the merging or to add a private note so any agent could understand that the merging was made by mistake.