What's the best and fastest way to naturally get rid of acne marks?

No easy fix: You need to manage your acne to prevent new lesions. If you have hesitated to get your acne treated effectively because of a preference for "natural" remedies, the retinoic acid derivatives and antibiotics that are mainstays of management are Mother Nature's gifts. The red spots are healing and cannot be altered. Don't try too hard to bleach the brown spots or it may make a mess. Best wishes.