Hi Martin, I'm affraid that for warranty reasons (purchase date) it will not be possible to re register. You could send an Email to Autel Tech Support. Maybe they can help you.
If not, try to contact the seller and ask him to modify his account, related to your purchased device. He can modifie his E-mail address by yours and also change the password. Once done, you delate your actual account. Then you enter with your E-mail address and the changed password from the seller. Check in "My Devices" if your purchased tool is there. If this works, you can change again the password from the seller. Just on condition: the seller must come from the same country as you: Country change is not possible in the Autel tool. Curious to know if this works because I intend to sell mine. Lood luck.
Garry.