From what I remember you have to have the old owner request that his account be closed so you can register it with Autel. The best thing to do is email support or call them and let them walk you through the procedure.
In a worse case scenario, I would think the seller would want his connection to the XStar terminated - more than the new owner. If I sold mine to someone who then did something stupid with it, the serial number(s) would link back to me.
Here in Canada come June 1st each UAV needs a registration number. You register the UAV and not yourself like in the US. So if you have a fly away, sell it or it gets stolen you have to let Trans Port Canada know so that number gets dropped. Unfortunately you cannot transfer numbers to a new UAV. Just a money grab from the government to pay for all this bull crap.
I whave one just for parts everything works great except the Gimbal. I replaced the wire on top of camera and now it connects and shows image . so camera work great and it flies great just no gimbal and I dont want to repair