Hi Niraj, Celine from Figma here, happy to help! Could you ask your students to check if their file is currently in their Drafts folder? Subscription plans are tied to teams, not individual email addresses (so anything stored in their Drafts is not related to their Education plan.)
They'll need to move the file to a folder within the team space that's linked to their Education plan in order to add videos. You can find more details here: Add video to prototypes.
If the issue persists, it would be really helpful if they could submit a bug report so our support team can take a closer look at it. To do that: Go to the Support Hub / Type “Report a bug” / Click Start a chat and select Enter / In the form, include the URL of the file and grant "Can View" access with support-share@figma.com. This allows us to reproduce the issue and investigate, thanks! 🙏