Hi! One shoulder stretch we do at our gym sometimes on on a beam, using a floor bar, or some sort of small weight. You also need a partner. Basically, you lie on your back on the beam and let your arms hang downward. your partner places the bar/weight in your hands, and you try to put it on the ground, or lower it as much as possible. You lift it up and lower it 5 times, and then you hold it in the lowest position for 10 seconds or so. Sorry if that was a little confusing.
About the weight:I really recommend a floor bar or parallette, don't use anything too heavy!! Good luck, I hope I helped!