Turn on the Instant Pot to the "brown/saute" function.
Add the sausage, breaking it up with a spatula into small pieces as it cooks, and cook until browned.
Add the olive oil add the onion. Cook until softened, about 5 minutes.
Add the garlic and season with Italian seasoning, salt, and pepper, and cook one more minute.
Add the marinara and water, stirring to combine.
Add the rigatoni but don't stir - just press the rigatoni pasta down to submerge it in the water. This prevents any burn notice from happening.
Cover the Instant Pot, seal the vent, and cook on HIGH manual pressure for 6 minutes. Do a quick release of pressure.
Stir in the heavy cream, mozzarella, and Parmesan until well combined.
Serve topped with fresh parsley. Enjoy!