Do contouring at the right place, only then the face will look slim.
The most powerful tool to make a round face look slim is contour. Apply a dark shade of contour or bronzer below the cheekbones, in a diagonal line from the ears to the mouth. Apart from this, do light contour on both the corners of the forehead and jawline. This makes the face appear less wide and longer. Keep in mind that do not blend the contour downwards, but blend it upward – so that the face looks lifted and sharp.