What are treatments for scoliosis with a 42 degree curve?

Depends. At 42 degrees with progression of curve and/or pain, a surgical recommendation can be made to treat a scoliosis. There are patients who do not have surgery, since their curves are stable with minimal or no progression. For patients with stable curves, non-corrective treatments, such as therapy or exercise, are based upon symptoms like discomfort.
How old are you? 42 degrees is significant, but it depends on if your curve is likely to progress.