Huh? How did you speedo get so far off that it needs that kind of manual calibration? ;-)
It's easy enough to get at the guage faces, but I would think twice (or more) about trying to adjust the needle. Better to let someone else do it, if you want it to be accurate.
Pull the headlight switch off (there's a release on the side you have to press), then undo the screws above the cluster and remove the bezel. The cluster comes out easily enough (do a search for white face guage installation, you can get pictures of how it comes apart).
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