Good to see you here in the Community. I'm by no means an accounting professional, but I do have some insight and resources to provide that can help get you on the right track.
Just to clarify, are you using QuickBooks Online Accountant (QBOA)? If so, then you could use the exclusive feature in QBOA to undo reconciliations without editing the transactions manually in the register. The steps below will guide you through the process:
Select the client from the drop-down list on the Toolbelt to open the client's company file.
Click the Gear icon, then choose Reconcile.
On the Reconcile an account page, select History by account.
On the History by account page, pick the Account and Report period to locate the reconciliation to undo.
From the Action column drop-down menu, select Undo.