dumbbell seated one arm rotate

Sit on a bench with your back straight and hold a dumbbell in one hand, resting it on your thigh. Raise the dumbbell up to shoulder height, keeping your elbow close to your body. Rotate your forearm outward, away from your body, while keeping your upper arm stationary. Pause for a moment at the top, then slowly rotate your forearm back to the starting position. Repeat for the desired number of repetitions, then switch to the other arm.