To clarify, are you using QuickBooks Online for Accountants (QBOA) to access a client QBO file? Only Accountant Users have the ability Undo entire reconciliations, and this can be accomplished with the instructions below:
Undo a Reconciliation using QBOA
From the company you're working in, click the Gear icon ⚙ > Reconcile.
Select History by account.
Find the reconciliation you'd like to undo, click the drop-down menu ⯆ and select Undo.
These instructions are also available from our guide on undoing a reconciliation for your convenience. If you're using QuickBooks Online as a regular (non-accountant) user, you'll need to change the reconciled status of each transaction individually. This article contains steps on how to do just that.
Should you still be interested in reaching out to our awesome Support Team, you can schedule a call-back using the following instructions:
Contacting the QuickBooks Support Team
From QuickBooks Online, click the Help (?) icon in the top-right.
Select Contact Us.
Enter what you need in the How can we help? field, and click Continue.
Click Get Callback, enter your contact information, and select Call Me.
These instructions are also available from our guide on contacting QuickBooks Online support for your benefit. Please touch base with me here if you have any additional questions or concerns, I'm always up to talk QuickBooks. Thanks for coming to the Community, cheers to a successful rest of your day.