I've got here a great method for you to correct your reconciliation beginning balance issue in QuickBooks Desktop (QBDT), @MJDuncan.

You can do a special or mini-reconciliation to correct your opening balance. It's a process that uses an "off-cycle" reconciliation date to make a correction. Let me guide you how.

1. Go to the Banking menu. 
2. Choose Reconcile.
3. Select the bank account with the transactions (original deposit) you need to reconcile.
4. In the Statement Date field, enter a date (between your last reconciliation and the next scheduled one) for an "off-cycle reconciliation." 
5. Enter the balance of your last successful reconciliation in the Ending Balance field, then click Continue.
6. In the Reconcile window, check off the transactions you are fixing and re-reconciling.
7. Make sure the Difference field shows $0.00.
8. When everything looks good, click Reconcile Now.

You can learn more about this process through this article: Reconcile previously deleted and re-entered transactions.

In case you're still having trouble fixing your opening balance, I'd also recommend letting your accountant check your transactions (i.e. deleted original deposit or the overpayment from 2017). This way, you can keep your financial data accurate.

Additionally, you can learn more about fixing beginning balance issues through this article: How to fix the beginning balance discrepancies when doing reconciliation. It includes topics about undoing previous reconciliation and how to redo it.

Please let me know if you have other reconciliation concerns or inquiries. I'm just around to assist you further. Take care always.