First of all, you are in the second or third grade, so losing weight must not affect your study and life.

Pay attention to your snacks in life and mind your mouth.

During the senior high school entrance examination, you need physical examination, you can practice long-distance running and actively participate in sports activities. This can not only lose weight, but also enhance physical fitness. To persevere, the weekly training volume should not exceed 5000 meters.

If you can't stick to it now, you can put it after the senior high school entrance examination, so it won't affect your study. After all, learning is very important.

(PS: It is impossible to lose weight quickly! I lost more than 30 kilograms in more than half a year, which has a great burden on my body and many sequelae.