If this payment is not yet reconciled in QuickBooks Online (QBO), you can go to your bank register and manually clear the transactions from there. Otherwise, you may need to undo it before you proceed with this month's reconciliation.
Here's how to manually clear the payment:
In QBO, go to the Accounting menu at the left pane to get to the Chart of Accounts.
Locate the account of the transaction and select View Register in the Action column.
Find the payment and repeatedly click on the status column (C for cleared, R for reconciled, and Blank for not reconciled/cleared).