Hi there, Pip and You. 

It's good to know that you've already checked and reviewed the register. I appreciate you for doing that.

If you didn't see an opening balance entry, you'll have to use your bank statements to make sure the opening balance is correct. Then, take note of the date and amount of the oldest transaction in the account. Once done, you'll need to create a journal entry for this. 

1. Go to the +New button.
2. Select Journal entry under Other.
3. Enter a date that comes before the oldest transaction in the account. This will be the opening balance date.
4. On the first line from the Account drop-down menu, select the account you want to enter the opening balance for.
5. We recommend adding a note in the Description field so you know what the journal entry is for.
6. On the second line from the Account drop-down menu, select Opening Balance Equity.
7. Use your bank statements to enter the opening balance. Note: Enter the balance of your real-life account for the date you picked as the opening balance.
8. Enter the debits and credits based on the type of account you entered on the first line.
   

Once done, make sure to manually reconcile the transaction in the bank register. This way, the beginning balance shows up on the reconciliation page.

Here's how:

1. On the left panel, select Accounting and select Chart of Accounts.
2. Click the Account history link of the bank account you want to reconcile. Search for the opening balance journal entry, and select it to expand the view.
3. Under the Reconciliation status column (Indicated by a check mark), click the blank field until you see an R. This reconciles the transaction. Select Save.

Please see sample screenshots below:

Also,  I'd recommend reaching out to your accountant for further advice on fixing the beginning balance issue in QBO, especially when creating a journal entry.

I'm also adding these articles about managing opening balances in QBO:

• Enter and manage opening balances in QuickBooks Online.
• What to do if you didn't enter an opening balance in QuickBooks Online.

Please post or comment in this thread if you have additional questions about opening balances or anything else. I'm always ready to lend a hand. Keep safe.