How do I undo a bank reconciliation.

I know how you can undo your reconciliation in QuickBooks Online (QBO),hlayna. I'll provide steps below. 

You can un-reconcile one transactions at a time. The option to undo a bank reconciliation is only available in QuickBooks Online Accountant. We can invite your accountant to perform the process. 

1. lick the Gear icon in the upper-right corner, and select Manage Users.
2. Go to the Accounting firms tab, and click the Invite button.
3. Enter the accountant's information.
4. Click Save.
5. Let your accountant undo the entire reconciliation.

If you prefer to do it by yourself, you can manually undo reconciliation from the bank register

1. Navigate to the Gear icon, then Chart of Accounts.
2. Locate the account that contains the reconciled transaction, and then choose View Register.
3. Find the transaction. If the transaction is reconciled, you’ll see an “R” in the checkmark ✔ column.
4. Click the transaction to expand the view.
5. In the checkmark ✔ column, select the box with the “R” until the box is blank. This removes the transaction from the reconciliation.
6. Select Save.

I've added here an article that will help you if 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.