The subclavius is a small triangular muscle, placed between the clavicle and the first rib
The subclavius muscle stabilizes the collarbone while the shoulder moves the arm. It also raises the first rib while lowering the clavicle during breathing.

With trigger points in this muscle, you might feel pain all the way down your arm.

It may even radiate into the thumb and first two fingers. The darker the red in the picture below, the more common it is to feel pain in the respective area when trigger points are present in this muscle.

This muscle can, among others, contribute to the following pain symptoms.
Pain in front of shoulder
Upper arm pain

Sit on the very edge of a thin pillow on the floor. The pillow will tilt your pelvis forward, helping you to sit taller and straighter. Legs are together and straight out in front of you. Place your hands on either side of your hips and slightly behind you on the floor.
To begin the stretch, press your palms into the floor as you draw the shoulder blades together and down towards the tailbone. Pull the belly button towards the spine to protect the low back. This stretch is all about the chest and you should feel no strain or discomfort in the lower back. The legs stay active the entire time. Look straight ahead ears are in line with the shoulders.

Do not slouch or round the shoulders. Do not lean too far back with the hands.
Take 8 to 10 deep breaths. Relax the arms to come out of the stretch


Self-massage with the fingers

Place the fingers of the opposite hand on the muscle.
Use your fingertips to pressurize the muscle and search for tender spots all the way along your collarbone.
Massage each of them with slow and short massage strokes by pulling skin over the muscle.
Usually you encounter the most painful spots towards your sternum and chestbone, respectively.

massage with ball:

The Subclavius muscle you will need a ball and a wall. Place the ball on the triggerpoint, just under your collar bone. Lean forward with the ball on the triggerpoint such that it is between you and the wall. You may tilt your torso to the “ball side” to increase the pressure. Hold for about 30 seconds and release.