Chop carrots into ¼ inch rounds. Chop celery into ¼ inch slices. Dice onion and mince garlic.
Make sure the stainless steel insert is in your instant pot. Turn on the saute function and let it heat up for about 2 minutes. Add olive oil and let it heat for about a minute.
Add onions, carrots and celery to the pot and cook for 2-3 minutes until softened. Add in garlic, dried herbs and a pinch of salt. Cook for another 2 minutes or so until garlic and herbs are fragrant.
Add brown rice and stir. Place whole chicken breasts on top and pour in broth.
Close instant pot and turn valve to "sealing".
Set the instant pot to cook manually for 12 minutes on high pressure.
Once cooking is complete, let the pressure release naturally for another 10 minutes. With a dish towel or oven mitt, carefully flip the valve to "venting" to release the remaining pressure.
Carefully open the Instant Pot away from your face. The chicken will be very tender. Shred chicken with two forks right in the pot, stir in fresh parsley if using, check for seasoning and add salt and pepper to taste.
Notes
If your chicken is frozen, make sure the breasts are separated and not in a frozen mass. The instant pot may take more time to come to pressure but the cooking time will be the same.