Clean and dry the inner pot of the Instant Pot. Select Saute function and heat remaining olive oil. Add pork, onion, bell pepper, oregano, cumin, salt, and pepper. Stir and saute, adding more oil if necessary, until pork is browned on all sides and vegetables are soft, 7 to 8 minutes. Cancel Saute function. Pour in remaining chicken broth and scrape the bottom of the pot with a wooden spoon to loosen any browned bits. Stir in reserved tomatillo puree.