Well, this happened to me recently even though I was following my usual recipe to a T. Little did I know that the chili powder and cayenne pepper I stocked our kitchen with here in Dubai were much more potent than those I had in Canada or Ireland so quantities should have been adjusted.
Well, with my mouth on fire just from taste-testing a spoonful, I quickly researched for a way to salvage my chili without having to start again from scratch.
Try one of these:
1 add a spoonful of sugar
2 add a tsp of baking soda
3 add a drizzle of honey
4 add a spoonful of smooth peanut butter
Any one of these should take down the heat. I had to try all 4. Finally, with the peanut butter, it was saved! I had to add a bit more salt afterwards but managed to get it back to being edible. whew!