For students, there are a couple options to permanently delete a video or simply hide from other students seeing it.

MyFlipgrid

Go to my.flipgrid.com to see all the videos you have ever recorded with your email. There, you can use the Actions button to Delete this Video or Hide this video.

Confirmation Email 

If you use your email to access the Grid, you will receive a confirmation email. At the bottom of the confirmation email, there is a link to deactivate your video.

Contact Your Teacher

To edit or permanently delete a video, students will need to contact their Grid educator. The educator can hide the video, permanently delete, or edit any information (name, email, title, etc.).