Sorry Ken, you cannot undo a merge (combining of 2 identical profiles) If you have accidentally merge two different people you will need to create a new profile for one. Then make sure the correct bio and sources for the new profile are transferred over, then save. Go back to the first and make sure only the right sources remain and save.
Please leave a message under ==Research Notes == header which site directly above Sources. Say what happened and why they should not be merged in future.