hello and welcome to HCM forum,
i would be glad to answer your query, first of all i would like to inform you that sun exposure causes a lot of skin pigmentation problems, in order to prevent that, one should always wear a sunscreen(30 SPF atleast),
For depigmenting the skin, you have a number of options, chemical peels
, MDA, lasers,etc.
but as you are interested in natural remedies, therefore i would recommend you to apply curd over the skin, leave it for half an hour, then wash it off.
Besan , turmeric or lemon application are also some of the natural ways to get rid of pigmentation.
but do not apply any of the ingredients on a broken or ulcerated skin.
kindly drink 8-10 glasses of water/day,
If in case you are looking for cosmetic treatments, then kindly visit your dermatologist
i hope i answered your query,
i wish you good health,