How do i remove a dark scar left from a pimple/boil?

Tincture of time: Most of the dark marks left when pimples go away are not scars, they are just dark marks. They go away by themselves, although they sometimes take their sweet time about it. Some of the topical medications prescribed for acne will hasten their resolution to some extent.

Pigmentation p/acne: Dark pigmentation after acne will usually resolve over time. Use of sunscreen will prevent prolonged pigmentary change. Topical acne preparations containing retinol, azelaic acid, kojic acid, and vitamin c help lighten dark spots. Hydroquinone is also an option.