The teres minor muscle is part of the rotator cuff and it externally (laterally) rotates the shoulder. It does so in combination with the infraspinatus, so I'm not certain that you can fully isolate it.
To Strengthen the external rotators together, you can do so with:
Because you say you have shoulder symptoms, a small towel roll between your chest wall and your humerus will reduce shoulder joint stress when doing the above exercises in the neutral or sidelying position.
Stretching - When the teres minor is tight it limits shoulder internal rotation. You can stretch the teres minor and infraspinatus with a broomstick stretch. Or this video gives some nice rotator cuff stretches with different ways to target the external rotators. You can also release the muscles using a tennis ball or theracane to massage the muscle.
If you haven't already, getting a full evaluation by a physical therapist or physio would be helpful to check for other contributing factors and stabilization of the scapula.