How to invite a parent to register as leader

I have a parent willing to volunteer. How do I get him to register as a volunteer in my.scouting without creating a new scoutbook account?

Should I just add his email as a lead and send the application, and then sort out accounts after? Or if I instruct him to log into my.scouting with same credentials, what does he click on to apply?

@BenMason Provide the parent with the Invitation Link or the Invitation QR code in the Invitation Manager at my.Scouting.

Ask the parent to log in to their my.Scouting account, first.
They should make sure their YPT is current.
Then click on the link from the Invitation Manager and apply as an adult.