If possible, this should be avoided. It’s better to return the belt and purchase a properly sized one. However, if you really want to make a hole in a belt, it should be done after careful measuring. Take note of the spacing of the other holes (it’s usually around an inch) and make an indentation where the new hole will go. Find a tool, like an awl or a nail, that matches the diameter of the other holes — then drive it through the top side of the belt to create the hole.