How to zoom in with Nikon d 800 movie mode?

Hi, I would deeply appreciate if someone could help me. I'm shooting a documentary with Nikon D800 but I can't seem to make a zoom in while I'm filming, or zoom to get extreme close ups.
I would deeply appreciate the help.

You turn the zoom ring on the lens… If you have a zoom lens mounted to the camera that is…

Extreme close ups will require you to use a macro lens like the 105 mm f/2.8 so you can maintain some distance from the subject

Zooming is rarely used when shooting video. The zoom lens is used to crop the frame without needed to move the camera, rarely anything else

When you see a video that is full of "zooms" it shows that the director is not an experienced video shooter.

Think of a zoom in the script as an exclamation point. After while, too many! Get boring and you lose your audience.

Take a look at this video shot using an older Nikon D7000. After viewing it with the sound off, look at your video script again and try to remove all but one or two zooms.

While the director of this video used three zoom lenses and one prime, you will not see any zooming going on (but for a very short few seconds at the end)

Most of the camera movements are either dolly's, pans, jib shots and a couple aerial shots using a small remote controlled helicopter.

EDIT: What accessories do you have? Do you have a Loupe similar to this?

http://www.luminous-landscape.com/reviews/accessories/hoodloupe-3.shtml

Here are some more links to the kinds of accessories you will eventually want if you intend to shoot video using a dSLR