Good day, @Thelma6658.
I'm here to help share some information about reconciliation in QuickBooks.
If you haven't completed the reconciliation yet, you can still edit the statement ending date. Just click on the Edit info button at the top of the Reconciliation page.
However, if you've already completed the process, you can no longer go back and change it. In this case, you'll need to undo the reconciliation. Let me route you to this article for the detailed steps: How to unreconcile a transaction or undo a reconciliation.
As always, you can contact our Online Care Support if you need assistance in going through the steps. Here's how to get their contact information:
Keep me posted how it goes. I'll be here to help if you have other questions about reconciliation in QuickBooks. Have a great weekend.