One possible reason why your gums are exposed is that the alveolar process of your chin is higher than the height of your lips. Generally, orthognathic surgery is needed to solve this problem (which will not be carried out here) and reduce the height of your alveolar bone appropriately.
Another possibility, do you think there are teeth protruding outward? Tooth protrusion can also lead to gum exposure, which can be solved by orthodontics.
Pull out a few premolars properly and then retract the front teeth, and the gums will naturally not be exposed.