What tendon are we talking about here? Usually for pain with overhead work, we're talking about rotator cuff issues, but do you know which rotator cuff muscle?
For many people, soft tissue work (Active Release Technique, Graston, etc), plus rehab work (rotator cuff work with a band, particularly external rotation work, light high-rep bamboo bar work, mobilization like shoulder dislocations with a dowel, etc) will go a long way towards helping. A good physical therapist or chiropractor could help with this. Just make sure you go to someone with experience working with injuries like this...a PT who does 99% of their work with geriatrics or a chiro who only cracks people's backs and does nothing else won't be helpful.