Unfortunately there are limited medical options.
Mostly you treat the symptoms of respiratory distress and try to encourage slow and deep breathing. Panic is the real enemy here.
Water reactivates chemicals; use baby shampoo when you shower hours later to get it out of your eyes
Most importantly: breathe. It will pass in a few hours.
If you must, don't use water: wipe away with paper towels or cloth.
The guidance is no, don't use it because it is not sterile and not shown to work
American College of Emergency Physicians recommends water or saline rather than milk.
abcnews.go.com/Health/baltimo…
But I you will have difficulty opening your eyes, let alone trying to remove contacts, in immediate aftermath
If you are entering situation where you might be tear gassed or sprayed just don't wear contacts