From within a bubble, hover over a media thumbnail and you will see a checkbox appear in the top left corner of the thumbnail. This checkbox, once checked, will put you in the Multi-Select mode and you will be able to tap multiple thumbnails to share or delete videos. The media items that you select will now display a checkmark in the upper left corner of the thumbnail and simply tap it again to unselect.
You can also tag, title or delete multiple items at one time.
How To Multi-Select & Take Action