If the area of the figure is a body part actor you can toggle its visibility in the heirarchy editor by clicking the eye icon next to its entry or by unchecking visible in that body parts properties. If the area is defined by a material in the material room you can enable transparency via material root node transparency setting value of 1. If neither of these are the case, open group editor, select the body part group in the dropdown which you would like to contain your new material and click new group. Enter name for your group. With your new group selected in the dropdown click the little + sign on the editor and select the polys that define your new material (they will be indicated red). Click the assign material button, name your material. Exit group editor. Enter material room, set value of transparency on your new material to 1.