Hi I have no experience with a dash cam. Maybe a member here has had a experience and will reply. My suggestion would be to go to the manufacture for advise.
Here's a link about dash cam!:wink: http://eyewitnesscameras.com/how-to-format-an-sd-card/
Assuming it's using a memory card or can be mounted directly to a PC like any other storage device, Recuva is my go-to data recovery tool, but you'll also find others. Many are paid however so watch out.