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.
Tonight I got a blue card from a Scout for the Citizenship in Society MB that apparently was finished back in 2024. I don’t see a way to enter that into the system. We had no idea he was working on it, as it was started in a prior unit that didn’t really use Scoutbook much.
It sounds like you go to the Eagle rank, click through to the merit badge, then enter completion? I haven’t run into this as yet, but I’m sure it’ll come up.