Buy a used product

Hey everyone, 

I am coming here because I need help. I bought an XR500 to someone else. The used product works perfectly but I can't set up it because the registration has already been by the precedent user. How can create my own login to connect and set up the XR500.

How it's going on when you buy an XR500 to someone and not in a store or website ?

Thanks for your help.