As others have said, you can't spot reduce fat. So any extra fat you have in that area just has to be burned off along with any other fat through the normal means (exercise and healthy eating).
If you do want to build the muscles there I do side extensions with a 5 lb dumbbell in my hanging hand.
I couldn't find a video or picture, but I use the same equipment as in this video, but I will rest on the side of my hip, with bottom leg forward on the foot pad and top leg back on the foot pad, and extend down with the weight and lift back up.
I hope this makes sense!