It's great to see you're checking up on the formatting needed for uploading transactions in QuickBooks Self-Employed. Doing that can save time when you're working with the information in your books, so I can appreciate why you'd want to take this step. I can help.
When uploading files for transactions to QuickBooks Self-Employed, the program calls for a CSV file type. This article touches on that, as well as highlights the options for manually bringing that information into the program: Manually import transactions into QuickBooks Self-Employed
If you're already using a CSV file and that's what you're interested in learning the formatting for, I recommend trying the steps outlined in this article: Format CSV files in Excel to get bank transactions into QuickBooks. The article is primarily tagged for QuickBooks Online, but you may be able to use it for QuickBooks Self-Employed as well since the bank feeds are similar for both programs. Give it a shot.
For further assistance, don't hesitate to reach out to the QuickBooks Self-Employed support team using the following steps.