How do I disconnect the electrical fastener/clip on top of the engine?

I'm replacing the valve cover gasket and there's a plastic electrical connection on top of engine. It's on the left side of engine (viewed from front of car) and immediately to the left of the plugs.

The wiring/connection goes through the valve cover. The electrical fastener/connection is about 3/4" on each side. Would you know how to disconnect the connection?