Wrap a towel around the rung of the ladder that is bent. Examine the direction of the bend.
Have an assistant hold the ladder in place and then strike the rung with the mallet. If the rung is bent downward, strike it from the bottom in an upward motion. Likewise, if the rung is bent upward, hammer it down with the hammer.
Wrap the towel around the side rail if this section, instead of a rung, is damaged.
Grasp the bent piece of the ladder with the vise grips and bend it into the position that will make the piece straight again.