Combine all ingredients in an Instant Pot or Pressure Cooker.
Set vent to sealing position and set time for 1 minute on porridge mode (see note).
Porridge mode will naturally release the pressure on it's own.
Adjust consistency with milk once the oatmeal is done.
Notes
Sometimes the IP can give a burn notice when cooking oatmeal. I don't have this problem in my 6 quart but I have had reports of it happening in the 8 quart. The oatmeal will not burn, but it may be golden brown on the bottom. This is normal and fine.