Help with video sound?

I took a video at a concert and I was too close to the speakers, and it sounds really bad! kinda muffled...I think you know what I am talking about! I was wondering if anybody knew how to fix this, or if you could recomend a free video editing software something like that. Or if this can even be fixed? Please recomend anything you can! Because I'm really mad and disappointed with the turn out of these! Thanks!