Solution for forgotten Apple ID

Apple can completely reset a device if a person can provide sufficient evidence of valid ownership. Do this online at: Activation Lock support request - https://al-support.apple.com/#/additional-support Apple says, "Proof of ownership documentation is required," but does not detail what currently constitutes proof. Apple may typically require the original receipt* issued by Apple or an Apple Authorized Reseller. If Apple resets the device this will give you access to the device but won't restore access to the account used to lock it. There is nothing that can be done to expedite an Activation Lock request.

*Apple recommends you "Keep your receipt after you buy an Apple device" --> Keep your receipt after you buy an Apple device - Apple Support

TO prevent this kind of thing happening again, look into management options.

Apple Business Essentials --> Apple Business Essentials User Guide - Apple Support

Apple Business Essentials includes all the features of Apple Business Manager and more. Apple Business Essentials is one complete subscription that seamlessly brings together device management, 24/7 support, and cloud storage so your small business can easily manage every employee’s iPhone, iPad, Mac, and Apple TV (that your organization owns)—every step of the way. Apple Business Essentials is currently available only in the United States." 20220427

Small business support by Apple --> Business - Small Business - Apple

Use Managed Apple IDs in Apple Business Manager - Apple Support

Use Managed Apple IDs in Apple Business Manager - Apple Support

Hi!

Unfortunately, the only way to do this would be to get into contact with him and ask him to remove the Mac from Find My. As you said, you're unable to contact him. In that case, there's nothing you can do to change the Apple ID associated with the Mac.