Add the oats, milk, water and salt to the instant pot. Place the lid on the instant pot and seal.
Press manual and set the cooking time for 3 minutes on high. Make sure the pressure valve is sealed. Once the instant pot beeps that the cooking time is up, let the oatmeal sit in the pot for 15-20 minutes for the pressure to naturally release, then flip the pressure valve to vent to release any remaining pressure.
Enjoy immediately with toppings of your choice. If you like it creamier you can add an extra splash of milk. Leftover oatmeal can be refrigerated in a tight compartment for 3-5 days.