The ability to unreconcile your bank statements is only available in QuickBooks Online for Accountant version. You can manually undo the reconciliation through your bank's register. I can guide you how to do it.
Go to the Accounting menu.
Select the Charts of Accounts tab.
Locate the account.
From the ACTION column, click View Register.
Identify the transaction to edit.
In the reconcile status column, repeatedly select the top line of the transaction to change the status. C - Cleared R - Reconciled Blank - Not cleared or reconciled
Click the Save button.
Also, I'd suggest consulting with your accountant so you'll be guided accurately in making changes in your account.
Always feel free to leave a comment below if you have other questions.