In the base of the slow cooker, combine the enchilada sauce, black beans, frozen corn, onion, garlic, chiles, salt, and pepper. Toss to combine.
2 cups enchilada sauce, 15 ounces black beans, 1 cup frozen corn, 1 small yellow onion, 2 garlic cloves, 4.5 ounces diced green chiles, 1 teaspoon kosher salt, 1/4 teaspoon ground black pepper