Hello there, @amanihaddad.

Let me share some information so you'd be able rectify the incorrect beginning balance in your account. 

The incorrect beginning balance of your previously-reconciled accounts depends on the total amount of all reconciled transactions, regardless of its date. You can review your bank's beginning balance last month and make sure that it matches your bank statement:

1. Go to the Accounting menu.
2. Choose Chart of Accounts.
3. Find the account on the list.
4. Click View register.
5. Search for the opening balance entry. It should have "Opening Balance Equity" in the Account column.
   
6. Take note of the date and balance.

If the opening balance in QuickBooks doesn't match your bank records, you can update it.

1. Go to the Accounting menu.
2. Choose Chart of Accounts.
3. Find the account on the list.
4. Click View register.
5. Select the opening balance entry to expand the view.
6. In the Deposit column, edit the balance so it matches your bank records.
   
7. Click Save.

You can undo initially reconciliation then, reconcile it again. However, if the balances match, you entered the opening balance correctly. You can proceed to Step 3 in this article: Fix issues the first time you reconcile an account in QuickBooks Online.

Also, you can browse this article to learn more about how you can manually undo your reconciled transaction: Undo and remove transactions from reconciliations in QuickBooks Online.

Lastly, I'd recommend consulting with an accountant so you'd be guided when reconciling your account. 

Always feel free to leave a comment below if you have other concerns or questions. I am always here ready to help.