Add the dry noodles to the Instant Pot along with the chicken broth, water, butter, garlic, salt and pepper. Stir together briefly.
In a seperate bowl, combine the grated cheeses
Close the Instant Pot and make sure the steamer valve is set to “seal”. Press the manual button and set the timer for 5 minutes, cooking at high pressure. When the timer is done, open the Instant pot steamer valve very carefully to quickly release the pressure inside the pot.
Add the shredded cheese and milk to the pot with the cooked noodles and stir until the cheese is melted.
Serve right away while hot!