I'd be glad to help you edit the password on the closed books in QuickBooks Online.
To do that, you have to log in as the Master Admin of the company. I'll show the next steps below:
Go to the Settings, select the Advanced tab.
In the Accounting section, enter the new password.
Select Save. Here's how it looks like:
Once done, you can track the transactions being added after the closing date by running an Exceptions to Closing Date.You also have the option to turn this off, however, I'd recommend reaching out to your accountant before doing it. They will assess your transactions and ensure you'll not get any error in the future.
I've added an article to help you on your future task with assessing your business financials: Learn the reconcile workflow in QuickBooks. This also contains how to resolve any errors you might encounter during the process.
I'll be here if you need further assistance or other questions with QuickBooks. Take care and have a wonderful day.