It will take time. The body has to re adjust how it processes insulin ie: sugar after the changes that steroids cause, like insulin resistance. Portion control and eat 5-6 small meal/snacks a day instead of 3 larger meals. The 5-6 small meals help to jump start the metabolism, and of course some kind of exercise.. walking is great. And yes plenty of water. I gained 150lbs due to high doses of steroids for a couple of years.. have been off the steroids for a while now and have lost 70lbs so far following that simple regimen. I hope this helps.. I wish you the best .
Eat small portions. Eat slow burning carbs (no junk food) - and lean protein. Eat within an 8 hour window - no food after 8 pm. Get a BMI chart and avoid consuming any foods that spike an insulin response - which in turn spikes cortisol - which takes glucose and stores it as glycogen.
Walk briskly for at least 20 minutes twice a day. Research anaerobic resistance training and join a gym with adequate equipment. Hire a trainer that know's what he or she is doing - and stick to their program.