After a cesarean section can I take slimming diet if breastfeeding?

Why not. Must take minimum required calories, supplemented with vitamins and minerals.
BF is slimming. If you breast feed & eat a balanced diet with a calorie load based on your pre-pregnancy or target weight you should be able to slim down naturally. Be sure to get adequate fluids, rest & vitamins & don't fall into the trap of eating extra for baby.