I will caution the so called treatment. Your question in unclear and some pigment change maybe due to (pre-)malignant change. To my knowledge so non-professional treatment are actually using carcinogen so without a clear information I will not suggest how to manage it.
Pigmentation of the skin depends on the post-trasncriptional regulation of MITF characterized by phosphorylation. I am now trying to reveal the detailed mechanism using 501MEL cell line about the regulation and stability of MITF in the presence or absence of stem cell factor (SCF; the ligand for CD117, also referred to as c-Kit).
That is why the down-regulation of phospho-MITF is the optimal therapeutic strategy to remove /cure such pigmentation
In India, you are aware that turmeric paste, leaf pastes of neem and henna and Aloe vera gel and its preparations are applied on the skin for treating skin problems. They are time-tested and safe. However, it is necessary to consult a doctor before regularly applying traditional herbal preparations.
I also read somewhere a paper on Aloe vera reducing dark pigmentation but I agree with the others, check the spot first. Rule out sinister possibilities.