I need to disable find my iphone but have changed Apple ID and email - I don't have access to the old email account for verification

I had an old iPhone 6 that bombed out years ago. I recently gave it to someone who had it repaired and is now trying to use it. However he cannot restore factory settings, as he is being told to turn off 'find my iPhone'.

This phone is still displaying my original email address as the Apple ID. I am no longer able to access this email, so I cannot have any verification sent to it.

How can I change the Apple ID on the phone, to allow him to reset everything that he needs to?

I have changed my primary email address and Apple ID details, but to add a new email address requires Apple to send an email verification to the old address, which I cannot access.

Just trying to help the guy get full functionality to the phone which he has worked really hard to save to have repaired.