Most will fade on their own, may take months to do so, and sun will keep dark.
If you are using a retinoid
for your acne
, that will also help to fade, as wil azaleic acid(another topical acne tx). Failing that, must use a bleahing cream, but that may make acne worse, and finally sometimes lasers, but their side effects are dark spots as well. Would coordinate with a dermatologist.