The rubber pads can we found under the scooter, near the hinge. We recommend folding the scooter to make it more visible. See photos below. Photo 1 has the pad in place, photo 2 is it missing and you'll see the black post you need to put the pad back on. There is a set screw for some models that holds the pad in place. If the pad fell out most likely you'll need to back out the set screw, put the pad back into place then tighten the set screw (see holes in photo 1 for set screw under the pad).
Photo 1 (pad in place, see hole where set screws sit under pad):
Photo 2 (pad out):