Please consult your gynac before starting any heavy exercises or wearing tight tummy binders, especially if you had a C-section. Your internal healing is much more important right now.
In my experience, it just took a lot of time. I massaged my belly with coconut oil daily and did simple home walks, but honestly, it takes about a year for the skin to shrink back a bit.
I used to cry looking at my loose tummy skin right after delivery, thinking it would never go away! But with time, light walking, and proper hydration, it naturally improved a lot. Give your body some grace, it took 9 months to stretch!
Since I am breastfeeding, my weight loss happened gradually on its own. Nursing actually helps the uterus contract faster, so just focus on good nutrition and let your body heal naturally.