What is a oil switch didn’t know there was one they said needs a knee one

The oil pressure sending unit, or switch, is located on the back side of the engine. The switch informs the car's main computer, the powertrain control module (PCM), of engine oil pressure. Sometimes the switches no longer seal and leak oil. I recommend having a professional shop perform the repair. You can find a reputable facility here: https://repairpal.com/repair-shops