It won't let me.
I have downloaded it.
And I can (apparently) copy it, but when I go to the plug-ins subfolder, I can't paste it there; the subfolder doesn't give me a "paste" option in the list of things that pops up when I right-click.
I can also move it from the download list onto the screen (desktop), but it won't let me move or copy it into the plug-ins subfolder.
Here is the list of what is in the plug-ins subfolder:
adjustable-fade.ny
beat.ny
clipfix.ny
crossfadeclips.ny
crossfadetracks.ny
delay.ny
equalabel.ny
highpass.ny
limiter.ny
lowpass.ny
notch.ny
nyquist-plug-in-installer.ny
pluck.ny
rhythmtrack.ny
rissetdrum.ny
rms.ny
sample-data-export.ny
sample-data-import.ny
sc4_1882.so
SilenceMarker.ny
SoundFinder.ny
SpectralEditMulti.ny
SpectralEditParametricEQ.ny
SpectralEditShelves.ny
StudioFadeOut.ny
tremolo.ny
vocalrediso.ny
vocalremover.ny
vocoder.ny
There is also a nyquist subfolder; here is the list of what is in there:
aud-do-support.lsp
dspprims.lsp
envelopes.lsp
equalizer.lsp
evalenv.lsp
fileio.lsp
follow.lsp
init.lsp
misc.lsp
nyinit.lsp
nyqmisc.lsp
nyquist-plot.txt
nyquist.lsp
printrec.lsp
profile.lsp
rawwaves
sal-parse.lsp
sal.lsp
seq.lsp
seqfnint.lsp
seqmidi.lsp
sndfnint.lsp
stk.lsp
system.lsp
test.lsp
upic.sal
velocity.lsp
xlinit.lsp
xm.lsp