Hi Jon,
It's a Perl script, so basically you just download the script and run
it. You can download the whole repository from
https://github.com/khaytsus/gqrx-scan if you click on the green "Clone
or Download" -> Download ZIP
You then run the script in a terminal with the proper options as
written in the readme file that you can also read on
https://github.com/khaytsus/gqrx-scan
The CSV file it talks about is created inside gqrx using bookmarks function.
There not much else to do than try it. If you hit an obstacle ask, but
be specific and include error messages that you get. I may be slow
with replies during the next few weeks but hopefully others can also
help you move forward.
Alex