My son forgot his Apple ID password

As indicated below, he will need to use to be able to answer his security questions satisfactorily to get his password reset. 

See If you forgot the answers to your Apple ID security questions https://support.apple.com/en-us/HT201485

He also can use Having trouble signing in/iForgot https://iforgot.apple.com/password/verify/appleid to deal with his security questions.

Being able to answer his security questions satisfactorily is critical. See Security and your Apple ID https://support.apple.com/en-us/HT201303

This document says “without proof of your identity via security questions and other carefully selected criteria, Apple Support can't help you reset a password or perform any other actions on your account.”

Thus, if he can't answer his security questions satisfactorily, then he will need to have an extenuating circumstance that will convince Apple Support to reset his password. I see no evidence that he has one. But, if he wants to discuss any possible extenuating circumstance with Apple Support, here are some support options he can use:

Get a call from Apple support to help solve your problem using this link https://getsupport.apple.com/?caller=kbase&PGF=PGF63005&category_id=SC0245&symptom_id=23362

Apple ID Support https://support.apple.com/apple-id

Apple ID account security for country-specific and region-specific help https://support.apple.com/en-us/HT204169

Get Support: We’re here to help https://getsupport.apple.com/. Go through the options to find the best support option.

See the information in If you forgot your Apple ID password - Apple Support