Pour milk into Instant Pot. Cover with lid, and secure the vent to the “Sealing” position. Press “Yogurt” setting, and press “More” to set pot to “Boil.” Instant Pot will start cooking within 10 seconds of the beep.
When boiling stage is over and Instant Pot beeps, let stand 5 minutes. Turn Instant Pot off, and remove lid. Carefully remove the inner stainless steel bowl, and transfer to a wire rack. Let stand, stirring occasionally, until milk reaches 115°F, about 30 minutes. (You can also place the bowl in a larger bowl of ice and water about 15 minutes, stirring occasionally.)
Place yogurt in a medium bowl, and stir in 2/3 cup of the warm milk. Return mixture to the stainless steel bowl, and place in Instant Pot. Cover with lid, and secure the vent to the “Sealing” position. Press “Yogurt” setting. (Time should say 8 hours. If it doesn’t, adjust the time to read 8:00.)
When yogurt stage is complete, turn Instant Pot off, and remove lid. Transfer yogurt to a clean glass or plastic container, and chill at least 6 hours before serving.