Let me provide some information about changing an incorrect date on a reconciliation,

We appreciate you carrying out my colleague's recommended solutions. We can still change the ending date if you haven't finished the reconciliation by returning to the reconciliation page. Then, modify the Ending Balance and End Date periods. Here's how it's done:

1. Go to Accounting on the left menu.
2. Click the Reconcile tab.
3. Choose the bank account from the Account drop-down list.
4. Tap the Resume reconciling button.
5. Tick the Edit Info button located in the upper right-hand corner.
6. Change the Ending Balance and Ending Date.
7. Press Save.

However, if the reconciliation has already been completed, the option to change the date in QuickBooks Online is unavailable (QBO). We can reverse the reconciled transactions. Let me demonstrate: 

1. Click Accounting at the left panel and choose Chart of Accounts.
2. Locate the account for the transaction and click View register.
3. Look for the transaction that you want to undo reconciliation.
4. In the check column, repeatedly click the top line of the transaction until the box is blank. This removes the transaction from the reconciliation.
5. Press the Save button.

To learn more about this one, see the Undo and remove transactions from reconciliations in the QuickBooks Online article. Once done, start the reconciliation again and enter the correct ending date. You can check the Reconcile an account in the QuickBooks Online article for the steps and details. Just in case QBO doesn't match your bank statement at the end of reconciliation, follow the steps in the Fix issues when you're reconciling accounts in the QuickBooks Online article to troubleshoot the issue. 

Feel free to visit our Reconciliation page for more insights about reconciling your bank account with QuickBooks.

I'd like to know how you get on after trying the steps, as I want to ensure this is resolved for you. Please reply to this post and I'll get back to you. You have a good one.