Well, if you think about it, everyone has their own way of handling things. But commonly, some people prevent heat exhaustion by doing the simplest things like maybe;
1. Drinking Water
2. Wearing Lightweight, Light-coloured and Loose-fitting clothes
3. Wearing wide-brimmed hats
4. Staying at home and turning the AC on.
If the person really cannot handle the heat exhaustion they should talk to their doctor and the doctor may recommend them a type of lotion, or medicine.
I Hope This Helps!