Pour 1 cup of water into Instant Pot pot, and then place in trivet. Place potatoes on top of trivet. Cover with lid, and make sure pressure valve is sealed. Cook on manual high pressure for 20 minutes. Do a quick release. Set potatoes aside, and discard water.
Turn Instant Pot to saute. Melt butter and whisk in 1 tablespoon of flour at a time until smooth. Add salt and pepper to taste. Once bubbling, pour in milk and bouillon base. Whisk occasionally until thickened.
Turn the Instant Pot to the keep warm setting. Stir in sour cream and cheese.
Finally, mash the potatoes with a potato masher to desired texture. Fold in potatoes, bacon, and green onions.