When treating frozen shoulder, our 3 main goals of treatment are pain relief, maintaining range of motion, maintaining strength. Most patients are not athletes or regular exercisers, so its unrealistic to give them a massive complex exercise program. One go-to exercise I've found particularly effective considering all of this criteria, is the simple shoulder press or a modification of it. Reaching overhead is a position that frozen shoulder patients consistently struggle with. The shoulder press is an excellent strength builder, and will often accompany some pain relief post-training.
In my experience, the sleeper stretch is really helpful for dealing with frozen shoulder. It focuses on the internal rotation movement that often gets tight with this condition. Getting the technique right is very important to make sure it helps and doesn't hurt, so it's best to do this with a physical therapist watching and giving tips. Here's how you do it: Lie on your good side, and put the sore arm at a 90-degree angle to your body. Slowly lower that arm towards your feet while you're lying down. Hold it there for a bit, then bring it back up. Use your other arm to help guide the sore one, but be gentle. Pushing too hard could make things worse. While this stretch is great, if you're not doing it right, it could actually make your shoulder feel worse. Always check in with a physical therapist before starting, and if it hurts while you're doing it, stop and talk to them.