Choose the appropriate weight. Grab the dumbbell using an underhand grip. Sit on the bench with legs at shoulder width, knees bent (90 degrees) and firm up your torso with pelvis in a neutral position. Put the hand with the dumbbell on your thigh with your forearm resting on it. The wrist protrudes over the knee (palm up). Torso is slightly leaning forward.
From the starting position guide the motion bending up at wrist while contracting the forearm muscles. Go back to the starting position bending your wrist slightly down. Do the required number of repetitions. Exhale while raising yourwrist and inhale while lowering your wrist.
Keep your torso firm, do not flex the upper (chest) portion of the spine (do not make a hunch).
Choose an appropriate resistance to start.