Can you start all over with a new MacBook Air from scratch?

Just bought a new MacBook Air for my Father. Was setting it up for him and made a huge mistake putting my UserID/email address and my password. When I went to use his email address or UserID with Apple we did not have the password for his account. My mother had set that all up before with the Mac mini and she has passed away.

When I tried to use his UserID/email address and clicked on "forgot password", the system wanted to send a link for him to reset the password. We had no way of receiving that link because he never had his mail set up on his Amazon Fire, cell phone or iPad. It was set up on the computer or Mac mini but he had taken it all apart, the monitor, Mac mini, mouse and keyboard and boxed it all up.

So I set up his new MacBook Air with my username and password. STUPID!

I've had this problem before when I bought a used MacBook Pro from a college student. The laptop still shows that person's name as the owner of the laptop. Never found a way to change it over to Me.

I went to Xfinity/Comcast just now and worked out a new password and got his email set up here with this new laptop. But I don't know if I can start all over with this new MacBook Air and put my Father's UserID and password into the system.

Please tell me this is possible!

Thanks,

Jeff