When you are absolutely sure that you have two people that need to be merged select the person that you want to merge into and then click People>Merge Two Specifc Individuals. A list of individuals will come up and you will need to find/select the second person on the list. This can be difficult if the names are spelled differently, if one person doesn’t show a last name, or if there are multiple people with the same name in your database. I recommend editing the names so that they are the same. Then edit the person that you want to merge and add an asterisk after their first name. Now it should be a breeze to find them on the list.
How To Merge Two Specific Individuals