Place 1 cup of water in the Instant Pot. Place wire grate in pot.
Set 4 pint-sized jars of milk in pot, uncovered.
Push the steam button and decrease the time from the factory set 10 minutes to 1 minute by pressing the - (minus) button.
Let run through this cycle. It will take about 15 minutes. As soon as it beeps, unplug it or it will keep warming the milk. Allow to cool about 15 minutes or until the lid will open. Don't vent it or your milk will boil over.
Open the lid and allow to cool to a pleasant "bathtub" temperature. Skim off any film that might have developed.
Add about a teaspoon of starter per jar. Use plain if you can, but I've been able to get away with using vanilla. After this initial run, you can use your plain yogurt you just made as a starter for the next batch.
Replace the jars in the Instant Pot (keep the cup of water in the bottom from before).
Press the "Yogurt" button. Allow to run for 8 hours. Cap the yogurt and place in the refrigerator. Keeps for several weeks.
If your yogurt is too runny, add a heaping teaspoon of powdered milk to your warm milk at the same time you add your starter.