Alternatively, you can invite an accountant to help you undo your previous bank reconciliation.
If you're using a different version, you can manually unreconcile your transactions. Here's how:
Go to the Accounting menu and select Chart of Accounts.
Locate and choose the account you’re working on, then click View Register.
Select the transactions you want to unreconcile.
Keep on clicking the R status repeatedly until it changes to blank (unreconciled) or cleared (C).
Click Save and click Yes to confirm.
Before completing any of these steps, I suggest consulting with your accountant. This is to make sure that all of your records are accurate and to avoid discrepancies.