Bowlegs are when the knees are curved out and space between the ankles is decreased. This condition is also called genu varum.
Arthritis, injury to the growth plate around the knee, infection, tumor, Blount's disease (a growth disorder of the shinbone), and rickets all can cause changes in the curvature of the legs. Exercise, stretching, strengthening, physical therapy, and vitamins makes the muscles and bones stronger but will not change the shape of the bones.
Gomukhasana alongwith Virabhadrasana and Parsvottanasana can help in improving body-gait to some extent, but not necessarily, and subject to the age (lesser age greater chance upto structural limit - the only change can be in strengthening the muscles of the knees only), dietary modifications, but it should be done with qualified yoga therapist. But before that one should practice suksham vyayam for better results. Sthula Vyayam like rekha gati can also be practiced to improve body gait.