How to re-activate a site into a paid site

Here's my situation: I created a subsite as the Super Admin and then gave that site membership privileges for 3 months. Then, it ran out and became inactive. My question is: how do I turn that site into a paid site and run them through Paypal. When I tested it, I logged into their dashboard using their credentials (not super admin), and was taken to the page to select the plan. But it also showed the full registration where they would have to create a username, password and all the other info. They already have a site, so is there any way for them to go straight to a Paypal checkout page and create the recurring payment for their existing site?
The subsite in question is

I have granted access to my dashboard.

I also see that we can transfer memberships to another site, so maybe I can have them go through the whole registration page and then transfer the membership to the existing site so they don't have to recreate what content they already have completed.

Thanks, Joe.