Hi, I'm John! I will help you with this.
The form is most likely asking for the Xbox Live Device ID, which is specifically labeled that way in your Xbox settings. You can find it by going to Settings > System > Console info.
It’s a unique 12-digit number that identifies your Xbox console on the Xbox Live network, so it helps Microsoft confirm your connection to the account you're trying to recover.
https://support.xbox.com/help/hardware-network/...
Take your time filling it out, and if anything else is unclear, feel free to reach out.
Click "Reply" below to let me know.
Regards,
John J.D.