If all of your invoices are “Finalized” then you would not be able to Edit your invoice batch. You need just one invoice in your batch to be in Pre-bill status in order to edit.
So just go to one of the invoices in that batch and press the “Unfinalize” button. Then after that, go back to the batch screen and click Edit. Make the changes needed and click Save. Then go back into that original invoice to Finalize it again.