Add milk to your Instant Pot. Cover with the lid and select the yogurt setting, make sure that it displays the "boil" message. And let the milk boil (it should take up to an hour).
Once the boiling is done, remove the lid and let the milk cool down. If you're running out of time, you can insert the stainless steel pot in an ice water bath.
Using a kitchen thermometer, the milk should reach a temperature of 100-110°F (37-43°C).
If a "skin" forms on the top of the milk, remove it using a spoon and discard it.
In a small bowl, whisk the yogurt with ½ cup of the boiled but cooled milk. Then stir it in the milk.
Return the stainless steel pot into the Instant Pot, select the yogurt setting at 8 hours (the pressure should read "normal", if it doesn't then adjust it). The longer you let it incubate for, your yogurt will be more tart.
When it's done transfer into containers, chill in the fridge until it's cold.
Notes
Use any percentage of fat to make yogurt.
If you decide to put the stainless steel in an ice water bath to speed up the cooling process, make sure to dry it well before putting it back in the Instant Pot.
If you leave the boiled milk on the counter to cool down to 100-110F, it should take around 1 hour.
The yogurt will last around 10-14 days if stored covered in the fridge.
If sweetening the yogurt, it's best to do so after it sets in the fridge overnight.
Do not use sweetened yogurt as a starter. The yogurt won't work in this case.
Make sure that the yogurt that you use as a starter has live cultures in it. Otherwise, the yogurt will not work!
Whisking in the yogurt in hot milk will kill the cultures. So it's very important to wait until the temperature of the milk is down to 100-110F before you add the yogurt.