Is plastic surgery effective to improve keloid c-section scar?

Yes: It is more likely that you have a "hypertrophic scar" rather than a "keloid scar." both can be helped by plastic surgeons who have many options available to them (both surgical and non-surgical) to improve the scar. Under the microscope both the hypertrophic and keloid scars look alike and their treatment is similar. Consult with a plastic surgeon to learn your options.

Yes!: Yes, surgery is an excellent option for improving your Cesarian section scar. I strongly recommend that you seek consultation with a board-certified plastic surgeon. Good luck!

It can be, but . . .: Keloids are more rare than hypertrophic scars and they're also much harder to treat. Proper treatment begins with a correct diagnoses of the type of scar. There are treatments for both! Hypertrophic scars respond better to treatments and to surgery, but keloids can also be treated with excision accompanied by corticosteroid injections. There are a number of emerging therapies as well. https://www.cosmeticsurg.net/blog/2016/03/24/keloids-hypertrophic-scars-in-plastic-surgery/