Interesting stuff, Thank you Marty for bringing it up. The professional aviation safety method of incremental exposure to scary stuff to build tolerance for the really scary stuff and a weekend of professional simulator training every 6 months doesn't scale down to us hobby pilots. Also have to point out, pledging allegiance to the rule book will not guarantee you don't experience a high stress event in the air.
Daily meditation is supposed to improve the ability to function under high stress, too hippy for me.
Stoicism also reduces stress. Just tell yourself you aren't going to survive this season/contest/instructional flight. And you will be more relaxed thus fly safer. Sounds dark. But it works. Those old guys knew a thing or two.
The Armed forces have had success with teaching simple breathing exercises. At peak heart rate people are uncoordinated, partially blind, sometimes deaf, and incredibly dumb.
Consciously regulating breathing brings people back to where they can function at a high level. Conscious breath control is probably the best, teachable, immediately available, universal technique for dealing with stress.
I have flown with a spire wearable. Spire measures respiration and can be set to alert you to mental states that correlate to breathing patterns. The stress alert while flying is mildly amusing. Comparing the respiration log and flight log postflight and seeing when there was focus, relaxation and stress is more interesting. Doubt wearables are useful as an inflight warning system.
Stress management is worthy discussion, except thinking about this stuff can be hard on the ego.