Ritz cruises just uses the Bonvoy program. So your Marriott Platinum status is your Ritz cruises status. Nothing else to do. So yes just fill out the form asking for a match to your Ritz Yacht Platinum status.

I had a Ponant number when I made my reservation- but had not matched status. You don’t have to wait until the status match to book. Though the Ponant match process was pretty quick.