What version of Adagio Ledger are you using? Making this mistake is very difficult to do in the current version.

Unfortunately, you're going to have to chat with your Adagio Consultant to decide the best way of dealing with this. I'm assuming that you have opened Next Year? Presumably, if you had closed this account last year with the wrong type, someone would have noticed.

You can unpost all the batches since the year was opened to get rid of the opening balances, and then change the account type and repost all the batches. That is, unless you have consolidated any of the accounts.