Combine the chicken broth, potatoes and garlic in a 6-quart Instant Pot. Close and lock the lid of the Instant Pot. Turn the steam release handle to “Sealing” position.
Press [Manual]; select “High Pressure,” and use [-] or [+] to choose 9 minutes pressure cooking time. When time is up, turn cooker off. Open the cooker using Quick Pressure Release.
Drain amount of liquid necessary for your own desired consistency. Draining half of the liquid should do the trick for most.
Mash potato mixture with a potato masher to desired consistency. Stir in yogurt, milk, and salt. Stir in chives just before serving.