Put the chiles in a small heatproof bowl, cover with boiling water, and let soak for 10 minutes. Drain and discard the liquid.
In a blender or food processor, combine the chiles, tomatoes, onion, garlic, and 1 cup of the stock. Blend until smooth.
Select Sauté on the Instant Pot® and heat the oil. Working in batches, brown the chicken on both sides, about 3 minutes per side. Transferto a plate as browned. Press the Cancel button to reset the program.
Add the chile purée, cumin, oregano, 1 teaspoon salt, and 1/2 teaspoon pepper to the pot and stir to combine. Return the chicken to the pot and add the remaining 5 cups stock and the bay leaves. Lock the lid in place and turn the valve to Sealing. Press the Soup buttonand set the cook time for 20 minutes at high pressure.
Let the steam release naturally, or for at least 15 minutes, beforeturning the valve to Venting to quick-release any residual steam. Carefully remove the lid and discard the bay leaves. Using twoforks, shred the chicken. Taste and adjust the seasoning as needed. Discard the bay leaves.
Ladle the soup into bowls and top with avocado slices, cheese,tortilla chips, cilantro, and a drizzle of sour cream. Serve right away.