Hello sir how to I lose my stomach fat?

Eat healthy. Stomach fat is made of white fats cells which respond most to diet and exercise. Cut out processed foods and saturated fats and weight will drop and fat will diminish. Exercise your abdominal muscles to further reduce fat around waist. All other exercise will help as well.
Diet and exercise. To lose fat/weight in general, it comes down to diet and exercise. If you specifically have issue with stomach fat, you can always consider liposuction; however, recommended still would be diet and exercise.