How do you straighten a warped recurve bow?
A slight limb twist can be fixed using this method: With your bow strung, hold the bow by the handle or the riser with your dominant hand. Use your other hand to grip the twisted limb tip and then slowly over twist the limb in the opposite direction, hold it for a moment, and then quickly release the limb.
Can you Unwarp a violin bow?
Yes, a bow can be re-cambered, but it requires some skill and I wouldn't recommend trying it yourself (edit: unless it is a cheap bow you want to experiment on and don't care if you wreck it). When the bow is made, the wood of the bow is bent into shape using heat, often by a careful application of flame.