What Could Cause Black Pigmentation At The Penis Head For The Past Few Years?

Age 20, Height 172cm , Weight 65 kgs, no medical history. Current problem is from last 4-5 years my penis head has black pigmentation i don t know how to remove it. How do I get the penis head in same unpigmented space. The upper skin is unable to cover the penis head due to black pigmentation. What can be done sir.