Set the Instant Pot to the ‘sauté’ function and heat the olive oil. Add the onion, carrots, and celery, cooking until the vegetables are softened, about 5 minutes.
Secure the lid of the Instant Pot, set the valve to ‘sealing’, and cook on manual high pressure for 15 minutes. Allow the pressure to release naturally for 10 minutes, then manually release any remaining pressure.
Open the lid carefully, season the soup with salt and pepper to taste, and stir well. If desired, use an immersion blender to purée the soup for a smoother texture.