I need to attach a four prong electrical cord to a Kenmore HE3 dryer. Where do the wires attach?

Red and Black go to outer terminals,
The're probably is a strap connecting center terminal to chassis for ground. Remove strap.
White goes to center terminal, and green goes to chassis for ground.

On a four wire cord just use the color code, white to white, red to red, black to black and green to metal frame. If the green wire is already on center or white white,remove it. To be safe, connect that green wire you took off white screw and put it together with the green wire on the cord that you screw to the frame or metal of dryer.