You can start by using any of the anti-stretch mark products available in medical stores (E.g. Renova Cream , Bio-oil, Palmers Stretch Mark Lotion).
Apply the product twice a day on these marks. Try this for 3 months.
(Before using any skin care product: always test it by applying a thin layer of it behind your ear or on your fore arm to check how your skin reacts to it.)
If you are not satisfied with results or you want fast results, you can see a dermatologist who can guide you on other treatment options like laser treatment and Microdermabrasion.