My tendons have been injured for a long time, what can I do?

Depends... Depends a lot on the type of injury and specifically are we talking about an open or closed injury? I.E did the tendon get cut or has it been strained and chronically inflamed, two very different types of injury. A lot will also depend on the location and the type of treatment up to now. Best to see a local hand surgeon for evaluation.
Seek medical attenti. Tendons that are injured for a long time need to assessed by a trained sports medicine physician. Physical therapy is the first treatment usually recommended. There are injection therapies such as platelet rich plasma therapy that can help.