Let me share some information about undoing reconciliation in QuickBooks Online.
The Undo option for a reconciled period is only available in QuickBooks Online Accountant. I'd recommend contacting your accountant and let them undo the reconciliation period at once.
Otherwise, you'll have to manually edit each transaction to undo the reconciliation.
Here’s how:
Click the Gear icon at the top and select the Chart of Accounts.
2. Locate the appropriate account for the transaction and select View Register on the Action column.
3. Identify the transaction to edit.
4. In the reconcile status column, repeatedly click the top line of the transaction to change the status. Then, click Save.
C - Cleared.
R - Reconciled.
Blank - Not cleared or reconciled.
You can use the screenshots below for visual reference,