It's unfortunate you waited so long, when you got the MRI did the doctor tell you how bad it is? Tendinosis can result in tearing if you try and power through it and make it worse. You're going to need to take at least a few weeks off anything that aggravates it and let the tendon heal itself. After its healed, this will probably require you visiting a PT or getting another MRI to see your progess, the second step is mobility work. Stretching and things to open up the shoulder joint capsule.
Then you move onto to things like external rotation, and other rotator cuff exercises to strengthen it back up. (Do these with a band to start). You should also try and figure out what caused it in the first place and correct that issue (ex. not setting the shoulders for a bench press puts a hell of a lot of stress on the rotator cuff) so that it doesn't get re-damaged afterwards.