I need to copy the right sound channel to the left sound channel on an .mp4 video
 

I have this .mp4 video file, but there is only sound on the right channel. Does anyone know what editing software I can use to copypasta the right sound channel into the left sound channel and then save the .mp4? Sure it's not surround sound or anything normal, but at least it's better than just watching the movie and only hearing sound come out of the right speaker.