On your iPad Air, tap on the select button and then tap on each video you want to delete. A trash bin will appear at the bottom right of the page. Tap on the trash bin and the selected photos will be deleted. The deleted photos will go to the Recently Deleted folder in the Photos app where they'll be automatically deleted in 30 days. The storage space used by those deleted videos is, however, released immediately for reuse. If you want to permanently delete anything in the recently deleted folder, the same process given for the initial deletion will work to permanently delete the videos.