I need help ASAP with my father’s apple id password

If he forgot the Apple ID (iCloud) password, enter the Apple (iCloud) ID, and click Forgot Password. See if he 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 he has 2 Factor Authentication enabled, if he can't recover the password using the steps above, he will need to use Account Recovery. The Recovery Process is an automated process and the length of time it takes can vary a lot. Apple ID Support can only answer your questions. They can't intervene in or speed up the process. The article below has some suggestions to shorten the time the process takes.

Apple ID - Recover your Apple ID with two-factor authentication account recovery.   *

If he has changed his password, has he followed the steps in this article on all devices/computers? 

What to do after you change your Apple ID or password - Apple Support.  *

See instructions in If you forgot your Apple ID password - Apple Support