Hi ljalex3g-bigpond,
Thanks for posting in the Community! You need to have transactions recorded in QuickBooks Online to be able to match them with your bank statement. If your bank statement has transactions on a specific period you're trying to reconcile, you can add them manually in QuickBooks Online by going to the + New button. Or if the bank account is connected to your online banking, you can manually import your bank transactions via CSV file.
For your reference, you can check this article: Reconcile an account in QuickBooks Online.
Feel free to drop a comment below if you have any other questions. Have a great day!