We can request from your bank if they can generate a copy of all your transactions in CSV format. If you can still log in to your bank's website, you can follow the on-screen instructions on how to download them as a CSV file.
Before we get them from your bank, let's check first if there are transactions that are already added in your QuickBooks account to avoid duplicates. Here's how:
Select Transactions from the sidebar menu.
Choose the account you plan to upload transactions into from the Account: All drop-down menu.
From the Date drop-down menu, select All.
Select the Date column header to sort the list by date.
Check the oldest transaction date in the account.
You can follow the steps below in uploading the transactions:
Open QuickBooks Self-Employed in a web browser.
Click the Gear ⚙ icon.
Choose Imports.
Select the account you want to add the transactions into.
Click Browse and find the file you downloaded from your bank.
Select the file and click Open to start the import.