How do I include a Collaborator and only have one person for each form?

Can you please tell me how do I include a Collaborator to have access to modifying only one of my Jotforms?

If you are referring to the new collaboration feature in the form builder, there is no way you can limit the number of access to the collaboration link. Once you share it, it will be available and shareable to anyone. 

https://www.jotform.com/help/419-Understanding-Form-Collaboration

You may consider sub-user account feature instead:

https://www.jotform.com/help/232-How-to-Share-Forms-with-a-Sub-Account-User 

With sub-user, you can add someone to edit your entire forms or specific forms. You are subscribed to our Bronze Plan which allows you to add up to 3 sub-user accounts.