I know how important to have the option to undo bank reconciliation in QuickBooks Online (QBO), Donna. 

Rest assured, I'm here to help you do it in QuickBooks.

I'd like to reiterate what my colleague mentioned about the undoing of bank reconciliation at once is only available if you're using the QuickBooks Online (QBO) Accountant version, they have a special reconciliation tool that allows them to undo the entire reconciliation. 

I'm adding this article for more guidance: Undo a client’s reconciliation in QuickBooks Online Accountant.

However, If you're using QBO,  you can follow these instructions to undo reconciled transactions one at a time:
 

1. Go to the Accounting menu. Then select Chart of Accounts.
2. Find the account and select View register.
3. To help you focus on this task, filter the register to only include the last 60 days of transactions.
4. Review the check column. If the transaction is reconciled, you’ll see an “R.”
5. Select the box and keep clicking it until it's blank. It removes the transaction from the reconciliation.
   
6. Select Save. Then close your register. 

I've added here an article that will help you in case you encounter reconciliation issues: Fix issues when you're reconciling accounts.
 

If there's anything else I can help you with, aside from reconciliation, please let me know by leaving a comment below. I'd be more than willing to lend you a hand, Donna.