As you can see there are many reasons for hot flashes. Hormonal, dietary, and probably others...., but what I understand you are asking about some sort of relief.
In the short run you can breathe with it till it passes, especially in public places. In the long run until you know what is causing it, splash cold water on your wrist, and face, an ice cube on my neck and chest helps me, and a cold shower believe it or not because it gets even hotter in the summer months here.
Other than that, you get really creative with relief techniques.
Jade