Add more ingredients to dilute the spiciness.
The easiest way to tone down a dish that’s too spicy is to add more ingredients to lessen the proportion of the spicy element. If it’s a soup or stew, try adding more liquid. Add more vegetables, protein, or starches, too — whatever ingredient you have extra of
Dairy is great at counteracting spiciness and can add a nice cooling effect. You can add milk, sour cream, or even a dollop of plain yogurt over each serving, but beware of adding and then cooking the dairy over higher heat, as it may curdle. Coconut milk technically isn’t dairy, but lends a great creaminess to dishes; plus it goes well with a lot of Asian flavors, if that’s the kind of dish you’re try to tone down.
Take this trick from Thai cuisine, which happily uses lots of chiles. To counteract spiciness, a lot of their dishes use a liberal amount of acid from citrus, vinegar, or even ketchup. A spoonful can really do wonders to balance out and counteract the spiciness.
Add a sweetener.
Like acid, sugar or other sweeteners add a different element of flavor that can tame spiciness. This one comes with a caveat, though, as you want to add very small amounts and taste constantly so your savory dish doesn’t end up tasting like dessert.
Add nut butter.
A fun trick I’ve read about is to add a spoonful of nut butter, like almond or peanut butter, to soups and stews. Apparently it will help mellow the dish out but won’t be really noticeable when you eat it. Has anyone tried this trick before?
Serve with bland, starchy foods.
Let’s say your overly spicy dish tastes perfect otherwise, and you don’t want to mess with it by adding other ingredients. My simple solution is to serve it with something bland and starchy so when eaten together, the spice is diffused a bit. Rice, pasta, crusty bread, or potatoes are all great candidates.