Desktop Admin Microsoft account tied to an old email with no other validation

Question

Hi,

My father created a Microsoft account years ago. The Microsoft account was added as his Admin account for his desktop computer. This Microsoft Account was only set up with the email as backup. He recently changed his email service and has no way to access the old email that was set for validation. Again, there is no secondary email or phone # attached.

I have tried to fill out the Microsoft form to add more details but keep getting denied because we cannot validate his identity via the old email.

We just want to either update the Microsoft Account set as his admin to add more validation methods so we can modify his computer OR change the current admin account to a new Microsoft account so we can modify the computer.

Please help :)