Ensuring data accuracy for your business is essential, and I'm here to help fix this for you efficiently, Dave.
In QuickBooks Self-Employed (QBSE), when you see a message saying that transactions you've tried to import already exist, it indicates that the system has detected that the transactions you are attempting to import are duplicates of ones you've already recorded in your account.
Let's verify your current transactions by filtering them by dates and amounts corresponding to the ones you’re trying to import. This will help us locate if they are indeed listed. Ensuring that your financial records remain accurate and free from duplicates. I'm sharing a screenshot for your visual reference:

If there seems to be a persistent issue or if those transactions aren't duplicates, consider contacting our QBSE support. They can provide more detailed, account-specific assistance and resolve this more effectively.
For a guide on importing transactions into QBSE, read this article: Add older bank transactions to QuickBooks Self-Employed.
To assist you in organizing your income and expenses more effectively, I’m providing you with this link: Categorize transactions in QuickBooks Self-Employed. This resource will guide you through categorizing your financial activities accurately.
Don’t hesitate to return to this thread if you have more questions about handling bank-related transactions, Dave. I’m always here to assist you