Try a simple doorway stretch: Place your arm against a doorjamb in the high-five position (that is, forming an L), your elbow bent 90 degrees. Step through the doorway until you feel the stretch in your chest and the front of your shoulders. Hold for 30 seconds. That’s 1 set; do a total of 4 daily.

Second:

 Weakness in the middle and lower parts of your trapezius and upper cervical muscles. Lying face down on the floor, place each arm at a 90-degree angle in the high-five position. Without changing your elbow angle, raise both arms by pulling your shoulders back and squeezing your shoulder blades together.

repeat by holding the pose for 5 second and 3 to 5 sets.

recommendation  by doing the stretching first and strengthening next will create a muscle balance to your upper, shoulder and neck posture.