Turn on a multi-functional pressure cooker (such as Instant Pot®) and select Saute function. Add oil, onion, garlic, and oregano; cook for 5 minutes. Add beans and water; stir. Close and lock the lid. Choose high pressure and set timer for 35 minutes. Allow 10 to 15 minutes for pressure to build.
Release pressure using the natural-release method according to manufacturer’s instructions, 10 to 40 minutes.
Remove the lid and check a bean; if not yet tender, close and lock the lid and cook another 5 minutes at high pressure.
Drain beans, reserving 2 cups of liquid. Return beans to pot and add salt and 1 cup reserved liquid. Puree using a stick blender, adding additional cooking liquid as needed. Keep warm using the slow cooker function.
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