I have white patches with rough skin between thighs and groin with itching
When I wash it the white patches disappear
When the skin is dry it will peel off as powder if I scratch
Please help me with some solution

It could be yeast, eczema, psoriasis, or any number of possibilities. Your doctor would know for sure though.

A common groin condition is tinea cruris (jock itch), a fungus, and you could try various creams and sprays available at a drugstore, if you can't get to a doctor easily.
But do see a doctor if that doesn't help.