Remove unwanted/hidden forms from website

Same issue. I have a client who has submission forms for a variety of job searches and receives those submissions via email. With this new feature, they're all saved in the Lists & Segments area under Form Submissions. For legal reasons, they do not want these stored online but I can't find a way to delete them. On main Lists & Segments screen there is a pop up menu that has a "Delete" option but it's grayed out. You can't select a submission or group of submissions. There are no options within the list of submissions or individual submissions to delete them. Seems like a legally necessary option.