First of all, it is forbidden to eat high-calorie and high-fat foods in the diet. High-calorie and high-fat food is one of the important reasons for human obesity, so we should eat more fresh fruits and vegetables. Carotenoids, cellulose and vitamins contained in fresh vegetables and fruits can effectively inhibit the proliferation of fat in human body, promote human metabolism, reduce human calories, and have a positive effect on weight loss. However, since you are still 12 years old and you are in the developmental stage, you need to supplement a lot of protein and nutrition, and you don't need to lose too much weight.

Secondly, do more aerobic exercise in sports, such as mountain climbing, swimming, jogging, yoga and so on. Aerobic exercise can effectively promote the flow of fat layer, accelerate the oxidation and consumption of fat in human body, and have a positive effect on weight loss.

Finally, you can do surgery to lose weight by liposuction. Surgical liposuction is usually carried out without improvement in diet and exercise. Surgical liposuction can quickly achieve the effect of losing weight. This kind of liposuction is not recommended. Surgery will be risky and life will be inconvenient. It is necessary to eat healthily and exercise to lose weight.

I hope it helps you.