Add the chicken breasts and 1 cup of the enchilada sauce to the Instant Pot. Lock the lid, set the valve to sealing, and cook on Manual/High Pressure for 10 minutes.
Let the pressure release naturally for 5 minutes, then quick-release the remaining pressure. Remove the chicken and shred it with two forks.
Mix the shredded chicken with about 1 cup of cheese and any optional mix-ins (onion, olives, jalapeños).
Warm the tortillas so they don't crack. Spread a thin layer of enchilada sauce in the bottom of a baking dish. Spoon the chicken mixture into each tortilla, roll up, and place seam-side down in the dish.
Pour the remaining enchilada sauce over the rolled tortillas and top with the remaining cheese. Bake at 375°F (190°C) for about 15 minutes, until melted and bubbly.
Garnish with sour cream, guacamole, salsa, pico de gallo, and cilantro. Serve and enjoy!