Preheat oven to 350°F.
In a large bowl, whisk together both cans of soup and the milk.
Add the cooked chicken to the soup mixture and stir to combine.
Spread chicken and soup mixture in a 3-quart casserole dish or a 9×13 baking dish.
Sprinkle with black pepper and just a dash of salt, if needed. Set aside.
In a 12-inch skillet, combine 4 tablespoons of butter, onions, celery, and minced garlic over medium heat. Saute until the onions and celery are soft and translucent.
Add the entire contents of the stuffing package to the skillet. Pour the water over the stuffing and stir to mix everything together.
Spread stuffing mixture over the chicken soup mixture in the casserole dish.
Melt remaining 4 tablespoons of butter and drizzle over the top of the stuffing.
Bake the casserole, uncovered, in the oven for approximately 30 minutes or until the stuffing is browned and the soup mixture is hot and bubbly.
Serve immediately.