Mostly have to un-think it. It's about learning how you respond to stress (when) and stopping the hormonal curve of that.
Yoga helps, and here is how.
Yoga postures are stressful positions in a controlled way (it's controlled application of stress). You can observe the way your body and mind interact while you are doing it (how your mind starts talking about what is going on). It's this loop that creates the "stress" at the emotional level that then goes bio-chemical.
By breathing, you can see the difference -- or rather observe -- the difference between "you" who is "ok under stress" vs your mind which is whining like a three year old refused a sweet at the grocery store (usually).
And when you can do that, you begin to unlock your stress response and then decrease your cortisol output over time.