1- Your starting position is to grasp dumbbell and use the opposite hand and knee on the flat bench to support the back.
2- Pull dumbbell up and to the side of your body until upper arm is just beyond horizontal, while looking straight ahead.
3- Lower the dumbbells down until arm is extended.
Tips and advises:
1- Make sure the elbow stays close to the side of body.
2- Keep your back straight.