Hi gunghoegrowers,
You can manually import the missing bank transactions or you can manually enter them in QuickBooks Online.
If you would like to import your bank transactions, first thing you'll need to do is to export the missing bank transactions from your bank's website in CSV file format. You can check on this article for more detailed information: Import Bank transactions via CSV. Once you've imported the transactions, you can categorise it and add it in QuickBooks. However if you would like to enter it manually, you can go to + New button and select the transaction type.
Feel free to drop a comment below if you need any help. Have a nice day!