Secure the lid and set the valve to sealing. Select manual setting for 10 minutes.
When it's done, you can do manual release right away, or just forget about it for hours. After the pressure has released, drain the little bit of water, add the butter and let it melt.
Stir in the milk and seasoning salt of your choice. (It's going to vary a bit in saltiness so make sure to taste them.)
Mash them well, taste for salt, put the lid back on and let the magical keep warm setting keep it warm for you!