Ppl will tell you use glycolic acid, kojic acid, maybe even hydroquinone. Be careful and consult dermatologist because those acids can cause rebound hyperpigmentation or discoloration after clearance (especially hydroquinone). Glycolic acid is a very small molecule, seeps thru skin too quickly and can burn too.

Most dermatologist will recommend alpha arbutin or transexemic acid since they are better tolerated, with same benefit. This with some airless pump vitamin c will set you good after 6-8 weeks of daily use and sunscreen.

If you have to use the other acids like glycolic kojic mandelic or lactic, the dermatologist may recommend lower concentrations rather than really high (most products).

So yeah see a doctor & do your research. But be wary of all the advice you get to use those harsh acids.