Batch custom genre tagging based on artist/s?

Hi, I'm not exactly tech savvy, so please explain like I'm 5...

I was told to download this program and run a script if I wanted to tag my massive library, but I don't even know how to use the program, run scripts and all the how to's don't really make much sense to me as someone who isn't used to....code?

What I'm trying to do is tag my tracks based on artist, also I want it to tag for all the artists on the track, not just the first one. So for example: if ARTIST is Y, tag GENRE field with Z, but tag from a custom text database that I made myself.

I tried to fiddle around with the "convert > text file - tag" option, but it doesn't make any sense at all to me, either that or it's not working after reading the how to on that feature.

That won't work as the function simply imports 1 line of text after the other, either in sequence, or, if you have a reference to the corresponding file, then by filename.

The easier way would be to filter for an artist e.g.
%artist% IS X
and then set the genre in the tag panel and save the modification.
Or you filter for missing genres with
%genre% MISSING
and sort by the artist column so that you have all files with the same data in ARTIST together in the list.
Then you set the genre as described.