There is a dial with a magnifier icon, but it doesn’t do the zooming. The lens doesn’t have zooming, it only has focus.
The Olypmus Digital PEN series cameras are interchangeable lens cameras. The camera itself does not perform the zooming — you can zoom only if the lens attached to the camera is a zoom lens.
It sounds like the lens attached to your camera is a prime lens. That is, it has only a single focal length, meaning it cannot zoom.