Otherwise, you'll have to manually remove the individual transactions from the reconciliations. Take note you can only unreconcile one transactions at a time to minimize the impact of the changes. Here's how:
Select Accounting from the sidebar menu.
Go to Chart of Accounts.
Find the account holding the transaction, then click View register from the Action column.
Select the transaction you want to unreconcile to expand the view.
Review the check column. You’ll see a letter R if the transaction is reconciled,
Keep click the checkbox until it becomes blank to remove the transaction from the reconciliation.
Click Save, then close the account register.
In addition, here are some articles that you can browse to help resolve common reconciliation issues in QuickBooks Online: