If the app or the web-based app won't let you, just wait until you're on the ship. It won't be a problem. We were in a suite in April and went to the Crown Grill on the first day and had no difficulty booking a first night res.
"Also like how it's so close to the Retreat Pool."
Different ship. Grand Class do have MDR on same deck, same side, etc. No Retreat Pool.
Royal Class ships have a Retreat Pool, but minis are on different decks. No guest cabins at all on the decks with the MDRs.
That's what I have to do. I've tried on the web-based app for both of us and it persists in showing our cruise for April '23 instead of the one that's booked next month.
As many have said...they fix one thing and break something else.