Hi mevenson511,
We're unable to change the End Date of a reconciled period, but you can redo the reconciliation to enter the correct one. Though this will not remove the original reconciliation report, you'll have a new one with a correct End Date. This article will guide you through the process: Undo or remove transactions from reconciliations in QuickBooks Online.
If you have an accountant user, you can ask them to undo your reconciliation as well. It's much faster.
Feel free to reach back out if you need more help with your reconciliation.
