Add all ingredients to the Instant Pot / pressure cooker - chicken breasts, lemongrass bulbs, chicken broth, apple cider vinegar, fish sauce, Chinese Five Spice, minced garlic, grated ginger, salt and pepper.
Close the lid to seal the instant pot. Make sure the pressure release valve is set to “sealing.”
Select the "Poultry" setting.
After the Instant Pot is done cooking, release the pressure. Once the pressure is released, open the Instant Pot and shred the chicken using a fork.
Serve with rice and pickled vegetables.
Food and Wine has a great description of how to trim lemongrass stalks - make sure to read this to properly use lemongrass.