This may help some:

If you have an account that is not connected to bank feed, but it was connected in the past and you want to bulk delete transactions, here is what you can do:

Create a csv file with Date-Description-Amount (add a few transactions). Go to tools-import data, click bank data, select file and choose the bank account that you want to bulk delete transactions. Accept the transactions.

Once uploaded Quickbooks will show the account in the bank feed, click on Categorized, filter by the dates you want to work. (make sure you disable your rules before you do this process). Select transactions you want to delete and click "undo". This will send the transactions back to the bank feed where you can exclude them.