Place the chicken breasts in the Instant Pot and pour in 1 cup of the chicken broth. Put the lid on and set the pressure release to Sealing. Select either the Pressure Cook or Manual setting and set the cooking time for 10 minutes at high pressure. (It might take about 10 minutes for the pot to come up to pressure).
When the cooking program ends, move the Pressure Release to Venting. After opening the pot, transfer the chicken to a plate or cutting board and shred the chicken into bite-sized pieces.
After returning the chicken to the pot, add the remaining 3 cups of chicken broth, tomatoes and their liquid, black beans, corn, garlic, chili powder, cumin, and oregano. Reset the cooking program by pressing Cancel and then select the Soup setting. Set the cooking time for 5 minutes at high pressure. (It will take about 20 minutes for the pot to come up to pressure).
After the cooking program ends, release the pressure naturally for 10 minutes. Move the Pressure Release to Venting to release any remaining steam.
Ladle into bowls and top with cilantro, tortilla strips, avocado, and lime wedges.
Video
Notes
STORE Instant Pot Chicken Tortilla Soup leftovers in an airtight container in the refrigerator, leaving off the tortilla strips to avoid sogginess. The soup will stay good for up to 3-4 days. To FREEZE, cool the soup to room temperature first, then freeze for up to 3 months in freezer-safe containers or Ziploc bags.To REHEAT, use the microwave, a pot on the stove, or the Instant Pot. For the microwave, heat in a microwave-safe bowl, stirring occasionally until hot. On the stove, reheat in a pot over medium heat, stirring occasionally until warmed through. In the Instant Pot, use the sauté function, stirring occasionally until the soup is hot.