The best way is to eat less every meal (70% to 80% full), and after two weeks, the stomach and abdomen will contract obviously (that's what I did, I experienced it myself)

If you exercise, you can lie on the bed (yoga mat is better), lift your legs, raise your hands, and pull your upper body up, down, up and down with your hands for 20-25 minutes, rest for half a minute, and then do another group. After that, you will find that the upper abdominal muscles feel sore, indicating that you can relax properly during exercise. Stick to it for a month and the effect will be very obvious.