Set the Instant pot to the saute function.
Saute onions in the oil for 3 minutes while you prep the garlic, carrots, and celery. Add them to the pot, and saute another 3 minutes.
Add the remaining soup ingredients besides the corn.
Give everything a good stir, and set your Instant pot to pressure cook on high. Pressure cook for 15 minutes.
Manually let the pressure out, covering steam with a kitchen towel. (Or allow pressure release naturally.)
Shred chicken with two forks and return it to your pot. Add corn, and return to saute setting for a few minutes just to heat through.