Hello frederickcm and welcome to the forum.
I am sorry to hear about the problems you are running into.
I think that you will need to get the registration Serial Number from the buyer. He/she may need to do a Licence Transfer:
https://www.ikmultimedia.com/faq/index.php?id=44.But I am not sure.
As this is primarily a user to user forum, someone-else may chime in. Meanwhile, the best thing to do is contact
Sales Support for some one to one help (US (East Coast) Business hours, generally). They will advise you of exactly what's needed. Response time generally is within 2 working days.