Preheat oven to 350F while you're assembling the tortillas.
Roast the corn. In a dry skillet (preferrably cast iron, but any large skillet will do), roast the frozen corn over med-high heat, until the kernels start to lightly brown. You don't need to thaw the corn first. Move the roasted corn to a bowl (this will become your filling bowl).
Cook the onions and garlic. Heat a little olive oil in a large frying pan over medium heat. Add the onion and cook gently until translucent and just beginning to brown. Add the garlic, stir well, and cook until fragrant and soft, 2-3 minutes. Transfer the onion and garlic to the filling bowl.
Add the shredded chicken to the filling bowl with the onion and corn. Stir to combine.
Drain the tomatillos if using canned (don't drain if using salsa). Add tomatillos (or salsa), green chile, and cream cheese chunks to a blender and pulse until just blended. If you don't have a blender, an electric hand mixer or stand mixer works; as a last resort you can mix by hand, but you must mix until the cream cheese is fully broken down and integrated.
Combine. Add about 1/2 to 3/4 cup of the sauce to the filling bowl and stir to combine. You want enough sauce that the filling holds together on a spoon, but not so much that it's runny.
Assemble. Pour a thin layer of sauce in the bottom of a 9x13 baking dish and spread it out evenly. Take one corn tortilla, spoon in about 2 tablespoons of filling (regular kitchen spoon, not measuring spoon), top with a small amount of shredded cheese, and roll. Lay the enchilada seam-side down in the pan. The enchiladas may unroll a bit; just keep tucking and squishing them together. As you go, some may split a little on top. That's fine. They still taste good. Keep rolling and adding enchiladas until the pan is full. Cram them together; they help keep each other rolled and supported.
Top. Pour the remaining sauce over the rolled enchiladas. Top with cheese.
Bake. 20-30 minutes at 350°F, or until the cheese is bubbly and any visible tortilla edges are starting to crisp and brown.
Serve. With pico de gallo, guacamole, sour cream, salsa, or whatever else makes you happy.