How I disassociate my email address from my R8000

I sold my Nighthawk and the new owner wants to register his email address to the device so he can take advantage of the USB functionality. Support is being beyond stupid and asking me to file a ticket even though the system doesn't let me do so. Is there a way I can take care of this myself, or do I have to keep hammering fruitlessly at the incompetent Netgear support team?