How can i reduce melanin in my eyes?

Not a good idea: The level of melanin in your eye (such as your eye color) is genetically determined and cannot be changed. Not sure why you would want to reduce the melanin in your eyes. Its both normal and healthy to have melanin. As a matter of fact, people who have no melanin have a condition called albinism and can have significant eye problems as a result of the lack of melanin.

You probably can't: If you are referring to the dark pigmentation that can occur on the while of the eye (sclera) similar to freckles or a birth mark, it's not likely that you can reduce or eliminate it except in extreme cases where surgery can be performed.