It seem that you have developed post inflammatory hyper-pigmentation or PIH. Do not apply any home remedies
which can aggravate the situation. You can apply creams such as Azelaic acid, glycolic acid
and kojic acid
can be used to reduce the pigmentation under dermatological supervision.
You can also go for latest treatment including chemical peeling under dermatological supervision. Use a good quality medicated sunscreen 3 times a day. Protect yourself from direct sunlight. Do not apply any hair oil on scalp
which are containing fragrance in it as it can also cause pigmentation on exposure to sun light.