There's a few ways to remove the link between a user and their social account. From the front-end, JFBConnect now has a menu item that you can create to let the user see and unlink any connections they have. From the back-end, you can go to the UserMap area, find the user and delete the connection.
Then, re-establish the connection with the correct user.
I hope that helps, but if you need anything else, just let us know.
Thanks,
Alex