What's the best way to cure tendon injury?

Most need surgery: Most tendon injuries require surgery to repair or reattach them to bone. Some will heal on their own, but in most cases there will be some loss of function (weakness, decreased movement). Also, in many cases the repair needs to be done within a week or two. Waiting longer results in scarring which makes the repair more difficult and less likely to work as well.

Depends on injury: A traumatic tendon injury could be a tear, which would likely require surgery. Most likely it's inflammation that will resolve with rest, ice, immobilization, oral/injectable steroids and/or therapy. See a board certified orthopaedic surgeon for evaluation and treatment.