Add plain greek yogurt to your Instant pot and whisk in your milk.
Put the lid on your Instant Pot and set the yogurt function to 24 hours.
When finished cooking, pour off any whey that is sitting on top of the yogurt. Be careful not to pour out your actual yogurt, though!
Lay your large dish towel or cheese cloth over a large bowl. I use my Kitchen Aid mixing bowl for this.
Pour the yogurt into the cloth and gather up the edges.
Secure the edges with a large rubber band, clean hair tie, or string, and hang the towel to allow the whey to strain off from the yogurt.
Strain for 4-12 hours to your desired consistency. 4 hours will yield a thinner "regular" yogurt consistency, whereas 12 hours will yield a much thicker "greek" yogurt consistency.
If you overstrain your yogurt, you can whisk back in some of the whey to thin it out.
Put the yogurt into your airtight container in the refrigerator for up to 1 week.