Great question, @trula.
You can re-open the closed periods any time by clearing the closing date. Then, you should be able to make changes to class as needed.
Once you've made your necessary changes, you can once again close out the year to close your books to prevent unwanted changes. This locks your books so no one can edit your accounting data before the closing date.
You can check out this article on setting a new closing date within your QBO account: Close your books in QuickBooks Online.
Let me know if I can help with anything else, I'm just a post away! Take care.
