We accidentally added a can of chopped tomatoes with chili peppers to a recipe. How can we reduce the heat?

Since I don't now what you are cooking it's hard to tell but if my chilie ends up a bit too spicy, I add sweet corn

Sugar is about the best way to counteract (or counterbalance) heat, but I wouldn't advocate adding it indiscriminately, and very rarely with tomatoes. Other than that, sheer mass is about all you can do- more of everything but the peppers- especially rice, potatoes and the like. The amount of pepper in a can of tomatoes shouldn't be too fierce in a made dish; perhaps you could just use it to build your tolerance.

In addition to the cream you could also try buttermilk or yogurt. Sometimes adding salt helps. You could also, depending on the dish, add some rice or potatoes, or serve it those heat absorbing carbs on the side.

There's really no hack to reduce heat, but you could make a partial or half recipe minus any heat and add it to the spicy version. It's hard to advise because you haven't said what the recipe is.

Add some cream, (or whole milk) The fat from the dairy combats the heat from the chili pepper.