There are many ways to gain weight, but the most important thing is to pay attention to diet and exercise. Here are some suggestions that may be useful:

-Increase calorie intake: eat more high-calorie foods every day, such as nuts, peanut butter, milk, meat, etc.

-Increase protein intake: protein is an essential nutrient for muscle growth. Protein's intake can be increased by eating chicken breast, fish, beans and other foods.

-Weight training: Weight training can help you increase muscle mass, thus gaining weight.

-Keep enough sleep time: Sleep is very important for physical recovery and muscle growth, so it is also important to keep enough sleep time.