Preheat the oven to 350°F (175°C) and spray a 9x13-inch baking dish with nonstick spray.
Place the chicken breasts in a large pot and cover with water; bring to a boil and simmer until cooked through, about 20 minutes.
Remove the chicken from the pot and shred it using a stand mixer with the paddle attachment or with two forks.
In the bowl with the shredded chicken, add the taco seasoning and the dry ranch salad dressing mix and stir until evenly combined.
In a small bowl, combine 1/2 cup bottled ranch dressing and 1/2 cup salsa; stir to make a sauce. Spread a very thin layer of this sauce over the bottom of the prepared baking dish.
Assemble the enchiladas: place about 2 tablespoons of the ranch-salsa sauce on a tortilla, top with a portion of the seasoned shredded chicken and a sprinkle of cheddar, then roll tightly.
Place each rolled tortilla seam-side down in the prepared 9x13 dish. Repeat with remaining tortillas and filling.
Generously sprinkle the remaining shredded cheddar cheese over the top of the enchiladas.
Bake in the preheated oven for 30 minutes, or until the cheese is melted and bubbling and the enchiladas are heated through.
Remove from the oven and drizzle additional bottled ranch dressing over the enchiladas before serving, if desired.