Add peppers, garlic, Italian dressing mix, and beef broth. Using a wooden spoon, scrape up any browned bits that are stuck to the bottom of the Instant Pot liner. Set Instant Pot to manual setting, high pressure, 90 minutes. Once the cook cycle is over, allow pressure to naturally release for 10-15 minutes before manually releasing the remaining pressure and removing lid.
Once cook cycle is over pressure is released, use forks to shred meat in the cooking juices.