Hello there, Jaff27.
Welcome aboard to the Community. I'm here to help you with importing your bank data into QuickBooks Self-Employed.
You can check the CSV template format to ensure the columns showing are correct. You can try using the three or four columns format for the bank file.
For your visual reference, I'm adding a sample screenshot down below:
Please also make sure that you have the correct date format: DD/MM/YYYY. In case you need insights about importing transactions, I'm adding this article:
Import transactions from earlier date ranges.
I'm always available here if you need additional assistance with importing bank transactions. The Community has your back.