what u have is post acne pigmentation and grade 1 acne scar
is depigmentory agent
it is very safe and work slowly
so u need to apply for long time
if u need fast result then retinoic cream or azelic cream work fast ,but irritation will be there and need to apply with caution .
better to consult dermatologist
procedure like peeling ,laser
,microderma will do better.