How to book an interior tour of Notre Dame?

No group tours are allowed yet. I would reserve a time and do some research about it be fore visiting. It is satisfying to look around and see what I have read about.
Being nerdish, or nerd-adjacent, I have read the history of countries I plan to visit, at least briefly, and find that I relish my travels so much more. Granted, you can't study the 2000+ year history of Turkey, but knowing some of it ahead of time really enhances one's time there.
Not for everyone, but I get a kick out of it. There is a lot of info out there.

Hi! Interior tours aren't allowed until June 9th. As an additional FYI, interior tours won't be allowed during Mass/service hours (approximately from 8:00am-9:00am, 12:00pm-1:00pm and 5:00pm-7:00pm), and/or on Saturday afternoons, and/or all day on Sundays.

The reservation system for tour guides/tour groups is planned to open on May 15th. As far as I know, if you want to book a tour, you'll need to book it through a tour guide/tour company, and they will make the reservation for the group.