Black marks which are left after pimples is called post inflammatory hyperpigmentation.
For the pigmentation sand scars there are different treatments
Scars are to be treated surgically like subcision, co2 laser, dermabrasion
Pigmentation can be treated with creams
But it would be possible for a dermatologist to prescribe creams if they can once look at it. If possible send a picture
Health Tips
Regular use of sunscreen will reduce post inflammatory hyperpigmentation ( black marks)