If you want to gain muscle, you should eat more protein food, and don't eat those fried foods with high calories and long fat. You can also eat some healthy foods with high fat content, such as avocados and nuts. Then do some resistance training. If conditions are convenient, you can go to the gym, practice equipment and lift dumbbells. If it is inconvenient, you can also do anaerobic exercise at home by your own weight, such as sit-ups and pull-ups. Although the effect may be slower, but stick to it and your body will be stronger.