We can redo the reconciliation, CLC4.
You're correct, the beginning balance will be affected once reconciled transactions are deleted or modified. You've mentioned that you deleted these transactions since they are not part of the period's reconciliation. We don't need to manually enter them again. Instead, we'll just redo the reconciliation to fix the beginning balances.
To do that, you’ll need to manually undo the reconciled transactions of that period one at a time. Follow Step 2 of this article to unreconcile transactions for your reference. Just a heads up, if you reconcile accounts every month and need to redo a reconciliation from three months ago, you’ll also need to manually unreconcile each transaction of the following two months.
You can invite your accountant and let them Undo the reconciliation period at once since this option is only available in QuickBooks Online Accountant. They can follow these steps on how to undo a client's reconciliation.
Once the transactions are being unreconciled, you can redo the reconciliation the usual way.
If you need more help with managing your reconciled accounts, you can always leave a reply here. The Community team always got your back. Take care!