First of all, do warm-up exercises, jump, move joints, and let your body sweat a little. Take a deep breath and do the following two exercises.

Thin arms stick to the fat on the shoulders, and the exercise method is simple: lift dumbbells!

Stand up straight with your legs open, hold dumbbells or mineral water bottles filled with sand iron nuts with both hands, straighten your legs and bend your upper body forward 90 degrees. At this time, your hands naturally droop, then open your hands to both sides and raise them above the horizontal line, then relax and let your hands droop. Repeat with arm strength for more than forty times.

After completing the above training, stand up straight, keep your back straight, hold your chest and abdomen, and raise the dumbbell above your head with one hand. At this time, pay attention to keeping the back arm close to the ear, then bend the arm back to the back of your head until the hand holding the dumbbell touches the shoulder of the other hand. Bend more than 20 times and do it with the other hand. (This movement is improved by yoga)

I'm using this method now, and the effect is still obvious. I hope you can succeed, too.