Masa can be found in the international food section of most grocery stores, but if you can’t find it you can make a flour roux on the stove instead. In a small saucepan, melt 4 tablespoons butter over medium-low heat. Whisk in 1⁄4 cup flour and cook for 1 minute. Whisk the roux into the soup, then press the Sauté button and simmer until the soup thickens.
Press the Sauté button on the Instant Pot® and heat oil. Add onion and cook until tender, about 5 minutes. Add cilantro, garlic, jalapeño, tomatoes, cumin, coriander, salt, and pepper and cook until fragrant, about 1 minute.
Add broth and chicken to pot and stir well. Press the Cancel button, close lid, set steam release to Sealing, press the Soup button, and cook for the default time of 20 minutes.
When the timer beeps, quick-release the pressure and press the Cancel button. Open lid and transfer chicken to a cutting board. Shred meat with two forks and set aside.
In a small bowl combine water and masa, then whisk into soup. Press the Sauté button and cook, stirring constantly, until the soup has thickened, about 8 minutes. Press the Cancel button.
Once soup stops bubbling, stir in chicken, cheese, and sour cream and stir until the cheese is completely melted. Serve hot with tortilla chips for garnish.