I haven't done this lens, but on Nikkors of this vintage, you typically have to pull up the silver lower barrel in order to expose the helical guides, which are accessed through a port on the side. Look for screws at the base of the barrel. You might have to remove the mount first. Typically 4 of the mount screws have to be removed, while the fifth should be left in place, since it holds the aperture spring.
On many, the entire inner barrel/optical assembly can be slid out in one piece by removing retaining rings at the front of the lens, but this model might not do so given its length.
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