You can use this one instead:
https://github.com/JoepVanlier/JSFX/...nd-time-window
It has a number of additional features and that's one of them. Right-click and drag to zoom.
If you don't use ReaPack to get scripts/JS plugins, you can download the files you need directly instead and install them manually.
The 2 files required are:
SaikeMultiSpectralAnalyzer.jsfx
colormaps.jsfx-inc
(Right-click and download both those files.) To install them in Reaper (again if you're not using ReaPack):
Open Reaper. Go to the main menu at the top. Options > Show REAPER resource path in explorer/finder. When the window opens, look for the folder named "effects". That is where you want to put these files specifically (or in a sub-folder within "effects"). Restart Reaper and the plugins will be available in the list.
I'd recommend adding ReaPack so that you can add scripts/plugins from many sources easily and have them able to be updated easily. See
this thread for info about ReaPack.