Welcome to the thread, CLG03. 

I understand the importance of having the Undo option during the reconciliation process. Your efforts in resolving this issue are much appreciated.

Please note that the Undo option is only available on the History by account page if you're using the QuickBooks Online Accountant version. 

In case you have the QuickBooks Online Accountant version, you can log in to your account to undo your reconciliation. However, if you have the regular version, you can follow the steps in this article to undo your transactions manually: Undo or remove transactions from reconciliations in QuickBooks Online.

Once you're done with the reconciliation, you can run a report to cross-check if everything is in order. For detailed instructions on how to run a reconciliation report, please refer to this article: How do I view, print, or export a reconciliation report?

If there's anything else I can help you in undoing your reconciliation, let me know in the comments section below. I'm here to lend a hand.