This is a natural and normal inquisitive beak exploration, with the beak and tongue (and their multitudes of nerve endings) being utilized by the bird to learn about its environment.
A parrot touching surfaces with its beak and tongue, sometimes with mild pressure. On human skin, this might lead to the curious removal of various bothersome things like scabs and tiny moles, but the bird is not trying to hurt. Skin exploration is often a sign of affection and frequently leads to allopreening.
Nothing, unless the beaking becomes painful. Prevent problems by limiting the scope and/or duration of beaking of human body parts to maintain control over the situation. Avoid providing a drama reward if the bird inadvertently causes discomfort. Calm controls can teach the bird the limits of what it is allowed to do with its beak. This is the equivalent of a child curiously touching things with his/her fingers.
Disclaimer: BirdChannel.com’s Bird Behavior Index is intended for educational purposes only. It is not meant to replace the expertise and experience of a professional veterinarian. Do not use the information presented here to make decisions about your bird’s health if you suspect your pet is sick. If your pet is showing signs of illness or you notice changes in your bird’s behavior, take your pet to the nearest veterinarian or an emergency pet clinic as soon as possible.