If you're using a device with a camera, it might be easier to select the "Take from Camera" option highlighted below. You'll record your video directly into the system and not have to worry about file size or type.
If that's not an option for you, there are a handful of ways to convert your file into an mp4. Depending on the device and the device and format your current file is in, you may need to search the web for the easiest way to convert that particular file into an mp4 file.
In your 5 second video, you'll want to make sure you state your Full Name, Date of Birth, State and the Conditions you are consulting for.