It's a common kitchen mishap to accidentally over-spice a dish! Thankfully, there are several ways to mitigate the heat, whether you're at home or in a restaurant. Here's a breakdown of effective techniques:At Home:
Dilution:

Add more of the base ingredients. For soups or stews, increase the broth, water, or stock.1 For other dishes, add more vegetables, grains, or proteins.2

Dairy:

Dairy products like milk, yogurt, sour cream, and cheese contain casein, which binds to capsaicin and neutralizes it.3 Coconut milk is a good non-dairy alternative.4

Acidity:

Acids like lemon or lime juice, or vinegar, can counteract the heat.5 Tomato-based products also provide acidity.6

Sweetness:

A small amount of sugar, honey, or maple syrup can balance the spiciness.7

Starches:

Starches like rice, potatoes, or bread can absorb some of the capsaicin.

Fats:

Adding healthy fats, like nut butters, or oils can help to dissolve the capsaicin.

At a Restaurant:
Communicate with the Staff:

Explain that the dish is too spicy and ask if they can make any adjustments.
They may be able to add extra ingredients or provide a side of cooling ingredients.

Request Cooling Sides:

Ask for a side of plain yogurt, sour cream, or rice.

Add Acid:

Ask for extra lemon or lime wedges to squeeze over the dish.

Consider Dairy:

If appropriate, ask if they can add a dollop of sour cream or yogurt. In some cases, they might be able to add coconut milk.

Bread or Starches:

Ordering extra bread, or rice can help to absorb some of the spice.

General Tips:
Taste as you go: When adding ingredients to reduce spiciness, add small amounts and taste frequently to avoid overcorrecting.
Consider the dish: The best method depends on the type of cuisine and the specific ingredients.
It is always best to ask restaurant staff how spicy a dish is before ordering, if you are sensative to spice.