I'm glad you've reached out to the Community, @general.
Once you disconnected your bank account with QuickBooks Self-Employed (QBSE), it will also be deleted the transactions. In order to retrieve it, you have to re-connect your bank account.
You can also import your bank transactions manually from the bank website and import them in QBSE using a .CSV file. Most banks allow you to export transactions to this file type.
To import your .CSV file, you can follow the steps below:
If you've been using a spreadsheet to track transactions, you can save or export the file to .CSV format.
Please know that I'm just a post away if you have any other concerns about downloading bank transactions. Wishing you and your business continued success.