How to whiten my inner thighs and groin and penis ...they are dark as compared to my body?

Lasers, pulsed light: Lasers and pulsed light are used for this. You need to see a dermatologist with expertise in this area.

Dermatologist: The genital area will often have a darker hue in general. Concerning the inner thighs not sure without additional history and examination. Suggest going to see a dermatologist or at least primary care physician for evaluation.