This is an advanced exercise where you turn the dumbbells up and out using a Preacher Curl bench for support.
Sit at a Preacher Curl Bench. Grasp a dumbbell in your hand with your palms facing up. Extend your arm fully along the bench.
Curl your arm up turning your wrist so it faces down as the dumbbell reaches your chest.
Pause for a moment and then return to the starting position and switch arms.