You can't Undo a merge. The only thing you can do is to create a new profile. I would recommend having separate browser windows open with both profiles so you can do a copy / paste, if possible into the new profile. You also may need to review the Changes Log which has the Merge statement. You can click on the 'merged away' profile ID, which will then show you the Changes Log for that profile. You can use the Previous to review the Changes, if you need to copy something from that profile that has been lost. Keep in mind that you will have a '-' sign in front of lines, depending on how you copy them from the left or a '+' if you are copying from the right side.
Hope this helps. If not, ask something more and send me a personal message and I can help you that way, also.