Press saute button (adjust to less if your Instant Pot runs hot). When the Instant Pot is hot add oil and diced onions. Saute onions for about 3-4 minutes until lightly browned. Add minced garlic and saute for 30 more seconds.
Add ground beef, chili powder, ground cumin, and oregano. Break up the meat into small pieces and saute until browned, about 4 minutes.
In a small bowl combine beef broth, tomato paste, and unsweetened cocoa powder until dissolved. Pour mixture into the Instant Pot to deglaze the pot. Use a spatula to scrape the bottom of the pot.
Add beans and stir until everything is combined. Then add tomatoes on top but don't stir. Layering the ingredients prevents getting the burn error.
Cover and cook for 10 minutes at high pressure. Natural release for 10 minutes and then quick release the remaining pressure. Remove the lid and stir until everything is combined.
If you want to add corn: Press the Saute button and add the sweet corn. Let simmer for a few more minutes until the corn is cooked through.
Season to taste with salt and black pepper and serve topped with sour cream and cheese.