Ice, rest, rehab
If this is truly acute tendonitis
, ice, anti-inflammatories, and unloading with a patellar strap.
Next, any faulty mechanics that may have led to the symptoms should be corrected. A sports med physician/physiatrist can determine if there is weakness of the core, or imbalance of the thigh or lower leg muscles. If chronic, new research has shown that it is not inflammatory, an treatment is differen.