The easiest way to fix this is to delete the linked DNA and then re-link it to the correct profile. It's best to log out of Family Tree DNA before re-linking, to ensure that you will link the correct kit. For more information see:
How do I delete the DNA test results linked from Family Tree DNA?
How do I link Family Tree DNA test results to my profile?
How do I link Family Tree DNA test results to a relative's profile?