Add the beef chuck roast to the Instant Pot.
In a measuring jug, mix the water with the birria seasoning or birria bomb until combined, then pour it over the beef. Add the tomato paste, whole onion, and garlic cloves.
Seal the lid and set the Instant Pot to HIGH pressure for 45 minutes.
Once cooking is complete, allow the pressure to release naturally for at least 25 to 30 minutes for the most tender result. You can quick release if needed, but natural release is recommended.
Remove the beef from the pot and place it onto a board or plate. Use two forks to shred the meat. It should pull apart easily.
Return the shredded beef back into the cooking liquid and leave on the Keep Warm setting until ready to serve.
Serve hot with tortillas and your favorite toppings. For a more traditional birria-style taco, dip tortillas into the top layer of the broth and fry lightly before filling with the shredded beef.