Turn Instant Pot to Sauté setting. Heat oil, then add onion, carrots, and celery. Cook, stirring occasionally, until vegetables are slightly tender, 6 to 8 minutes. Add garlic and thyme and cook until fragrant, 1 minute. Add bay leaves if using, then add chicken breasts and season generously with salt and pepper. Add broth and water and close lid. Set Instant Pot to Soup setting and set timer for 7 minutes.