Uneven skintone on arms helppp

So I rarely wear sleeveless because I'm kinda insecure about being a lil on the chubbier side. But recently I've decided that I would wear sleeveless more often. I kinda have uneven skintone on my arms. Not sure if its sun tan or other pigmentation. Is there any remedies or solutions for this? I have an upcoming event in a couple of weeks and am planning to wear a sleeveless blouse as well. Need to look goood. Thanks in advance :)