first rule to reduce pigmentation
is a good sunscreen. Please select one from reputed company which is gives you protection from both uva
and uvb protection.
There are lot of skin lightening creams available which should be used under doctors supervision as unsupervised application can lead to severe skin damage.
You can apply lemon mixed with water to begin with and then undiluted fresh lime as skin gets used to.
But please remember most important is sun protection for pigmentation.