K-wings in bees are a bit like a limp in a person – they are a symptom, not a disease. To find out the root cause we have to delve deeper into the various diseases bees can suffer from.
It is clear that Deformed Wing Virus is transmitted by varroa mites. Hence deformed wing virus treatment is really just varroa treatment. This is a nice overview of varroa mite control methods.
When a bee has so-called K-wings, the rear wings will spring backwards making a K shape if you look at the bee from the top. Because the bee cannot clip its wings together, it is unable to fly.