Add milk to the Instant Pot insert, place the lid on, and set the valve to the sealing position.
Press the yogurt button until 'boil' appears on the screen.
Once done, perform a quick pressure release, stir the milk, and use an instant-read thermometer to check that the temperature is at least 180 degrees F / 82 degrees C. If it hasn't, place the lid on and run the boil cycle again.
When the temperature is 180 degrees F / 82 degrees C or higher, take the Instant Pot insert out and place it in an ice bath (use a large bowl or pot partially filled with ice and water) to cool it down to between 110 degrees F / 43 degrees C and 115 degrees F / 46 degrees C. Check the temperature every 5 minutes or so.
Add the yogurt starter to a medium-sized mixing bowl.
Once the milk has reached 115 degrees F / 46 degrees C, remove about a cup of the milk, and whisk it into the yogurt starter.
Add this starter mixture back into Instant Pot insert, whisking until fully incorporated.
Put on the lid and lock. Press the 'yogurt' button and set to 'normal' for at least 8 hours, up to 12 hours, depending on how thick you want the yogurt to be (more time will make a thicker yogurt).
When complete, open the lid and transfer the yogurt to Mason jars, then chill the yogurt in the fridge until completely set, approximately 4 hours.