Add all ingredients to the pressure cooker and stir to mix
Close lid on Instant Pot® and make sure the pressure release valve is in the sealed position
Press the 'Manual' button and adjust the cooking time to 18 minutes
When the alarm indicates the cooking cycle is complete, press 'Cancel' to turn off the warming mode and allow pressure to release naturally (30 to 40 minutes)
Once pressure is released, open the pressure cooker and stir the mixture with a large spoon – using the back of the spoon to mash the tomatoes