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.
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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.