Please Read this Advice on Playing in the Heat
1. Schedule to play in the morning or later evening and avoid the hottest part of the day.
2. You should walk onto the court well hydrated.
3. You should have 3x the amount of liquids that you normally would bring.
4. You should take longer breaks between points and games. Both players need to respect this guidance.
5. Please defer to play a 3rd set tie-breaker instead of a third set.
6. If you start to feel weird, end the match right there and respectfully let your opponent know. They should understand that the league isn't about forcing you to play. You can always meet up again another day to finish the match.
One caveat, if it is a playoff match than retiring is considered a win for the other player. But, don't be an idiot and stay on the court longer than you should, listen to your body.