Place cubed potatoes in Instant Pot. Pour chicken both over potatoes.
Place lid on, twist to close. Make sure valve is on 'sealing.' Press manual, and set for 10 minutes.
When timer goes off, do a quick release and carefully remove lid (wear an oven mitt!).
Use a potato masher or hand mixer to mash potatoes. Add milk, butter, cream cheese and sour cream.
When the potatoes have reached the consistency you like, add salt and pepper to taste.