In the bottom of your Instant Pot, place your potatoes so that they are level. Put in the metal rack on top of the potatoes pour in one cup a water and set aside.
In a medium sized bowl, stir together the beef, eggs, chopped onion, oatmeal, ketchup, salt and pepper, 1/2 of soup, and 1 T Worcestershire sauce with your hands (it really is easier that way). Mold and put into a pan or foil shaped like a loaf pan. In a small bowl, stir brown sugar, the rest of Worcestershire sauce, and rest of the soup and pour over top of loaf.
Close the lid and make sure the knob is on "sealing." Push the manual button and cook for 25 - 30 minutes. If your meatloaf is thick, you will want to stick with the 30 minutes.
When it is done cooking, move the knob over to venting (quick release) and wait for the steam to come out.
Remove the pan (or foil loaf) from the pot. Add butter, milk, salt and pepper on top of the potatoes. Mash to desired texture. Serve with potatoes with meatloaf.