Post-inflammatory hyperpigmentation (PIH) regardless of site is best managed by controlling any ongoing skin inflammation causing the pigmentation.
The actual PIH should be best left to resolve spontaneously over the next 6-18 months. PIH on the face tends to clear faster compared to those on the extremities.
Lightening creams containing hydroquinone and laser treatment may help to hasten the clearance process, albeit unpredictably and variably.