Hi @Berway72,

Greetings from Freshworks community. To convert a collaborater into a agent, I suggest you to delete the user who is a collaborator so that their profile would be updated as a contact.

By Design, if you delete an agent or a collaborator, their profile would be converted into a contact . Later you can search using their email address and use the option "Convert to Agent" > Choose Full Time so that you can convert them into a support agent by utilizing your available seats. 

Yes i thinks there is a simple way of it.