Welcome! This forum has a treasure trove of great info – Scouters helping Scouters! Just a heads up, though - all content, information, and opinions shared on this forum are those of the author, not the BSA.
I was updating Scoutbook and accidentally advanced a Den twice and now i can’t figure out how to “de-advance” a den.
There seems to be a way to go back in rank of each scout in the Den, but still can’t get the Den to go back to prior rank. Do i need to create a new Den and transfer scouts?
Creating a new den and transferring them in from that new den’s Roster is the best way to proceed. Don’t try ending the memberships one at a time. That will just confuse things, and potentially drop scouts from your Scoutbook roster.