I am a dark skin person female and the skin around my genital area is white. What is the cause of that and how can I fix it.?

White spot. See your dermatologist for an appropriate diagnosis. Vitiligo is a condition where there is loss of melanocytes and the skin gets very white. Often it starts around body orifices. Your doctor can look at your skin with a woods light and see if there are lighter spots developing anywhere else. Treatment depends on what the diagnosis is.
Vitiliggo or LSA. Lichen sclerosus et atrophicus are usually whitish skin elevations and may respond to steroid cream. Can resolve spontaneosly in young , but, not in mature women. Vitiligo is a condition of skin depigmentation. It is quite benign and does not respond to any treatment. Suggest you consult with a gynecologist.