Those "black bars" are actually unused space. There's not anything there. So there's nothing to "fix." Typically you get the blank space on movies that have an aspect ratio of 2.35:1.
If you choose to modify the video to fill up the blank space you will distort the picture and lose some of the image. If you absolutely must fill your screen with the picture you should encode the video file at the correctly aspect ratio then use your TV to zoom the picture. This will ensure the picture will, at least, not be distorted. But when you do this you will also be losing part of the image on the sides, and possibly the top and bottom.
Regards,
Michael