Well, as a novice there's a lot to learn 
A couple of things:
- The shell environment in KM is different to that in Terminal insofar as KM's shell has a bare-bones path environment set up. As a result it won't know where yt-dl is installed on your Mac. The easiest way round this is to specify the full path to yt-dl.
- You're not providing the video URL to the KM action.
Searching the KM forum for yt-dlp came up with this:
Take a look as it should help you. You should also study the wiki page I linked to previously as it contains important information about paths.
You might also want to search the KM forum for "YouTube" so see how others use KM to download videos.
Sorry I can't be more expansive with my help as I'm really time-constrained right now.