How do I fix a "missing header" error in the MLV App?

[hungrygeneraiton]

I just shot a video on a 5d Mark III at 12bit lossless and when I went to load it I got the error "missing header". Is there anything I can do to recover the file? Also is this indicative of a bad card?

[Walter Schulz]

Backup file. Backup card image (How-To -> Web search).
Use h2testw (Windows) or F3/F3X (macOS/Linux) to test card.

[hungrygeneraiton]

The exact error in the MLV App is "File header is missing, invalid MLV". Thought that might be helpful for Google later if people have the same problem.
I did google backup file and backup card image and I know how to do both but how does that help me repair the file? I'm missing something.

Thank you for the card tester!! I don't think it's compatible with Mac OS Catalina unfortunately but I'll dig around and see if I can find something!