See if he can recover the ID/password. Use every email address he can think of.
Apple ID - How to find your Apple An iCloud e-mail address is an Apple ID.
Apple ID - Find
If he forgot the Apple ID password, enter the Apple (iCloud) ID, and click Forgot Password. See if yhe can get a Rescue or Notification email option if necessary. Link to contact Apple Support at the end of the 2nd article.
Apple ID - Manage
Apple ID – Forgot Password
If necessary, if he is the original owner, contact Apple. Apple can remove the ID if provided the required paperwork.
Request additional support for unlocking your device
Either take the device, the original purchase receipt with the serial number, and a photo ID to the nearest Apple Store (if it has reopened). Call the store before going to make sure they can help.
Genius Bar Reservation and Apple Support Options - Apple.
or contact Apple ID Support.
Apple ID - Official Apple Support.
Contact Apple for help with Apple ID account security - Apple Support. (Link doesn’t always load)
Get Support https://getsupport.apple.com Work through the screens to get a chat option.
Apple Support schedule phone call
https://twitter.com/AppleSupport