Hi and welcome to HCM,
Reducing weight can be a little tricky while your immune system is not doing well. Make small realistic goals and work toward achieving it.
First of all keep calories under count. Use online apps like healthify or calorie counter and cut down the calories slowly. Shift towards low fat diet, eat more fruits, fibers and have divided meals instead of large meals.
Start with minor exercises like yoga
and slowly increase your time for various power workouts.
Dont do any fad diet to try to reduce weight drastically. Will do more harm than good.
Hope I helped. All the very best