Preheat the oven to 375°F (190°C).

In a large bowl, mix together the shredded chicken, ricotta cheese, mozzarella cheese, Parmesan cheese, Italian seasoning, salt, and black pepper until well combined.

Carefully stuff each manicotti shell with the chicken mixture using a spoon or a piping bag.

In a saucepan over medium heat, melt the butter.

Add the minced garlic and sauté for 1-2 minutes until fragrant.

Pour in the heavy cream and bring to a gentle simmer, then stir in the Parmesan cheese, salt, and black pepper until combined and smooth.

Spread a thin layer of Alfredo sauce on the bottom of a baking dish.

Place the stuffed manicotti shells in the dish and cover with remaining Alfredo sauce.

Sprinkle additional mozzarella and Parmesan cheese on top.

Cover the baking dish with foil and bake in the preheated oven for 20 minutes.

Remove the foil and bake for an additional 10 minutes, or until the cheese is bubbly and golden.

Remove the dish from the oven and let it cool for a few minutes.

Garnish with chopped parsley before serving.