Go to your "\GPL\Tracks" directory. You should see a directory for every track you have installed. Create a new directory under "tracks" named "aindiab", one word, no spaces. Then use the 7-zip compression utility to unpack the ".7z" file into your new directory. When you have done that, start up GEM and click on the "Seasons" button. Pick a season file in the right-side window, and then scroll through the left-side window until you see your "Ain Diab" track. Highlight it, and then click on the "right arrow" button between the windows to add the track to your chosen season file. You should then be able to click "Ok" to go back to GEM, select the season file you just edited, start GPL and select the track.
I hope that helps!
Edit: I mentioned the "7-zip" compression utility above. There's actually a better one that I've just remembered. "WinRar" handles the ".7z" file format too, plus a lot of other compressed file types.
Edited by Saiph, Aug 09 2018 - 08:07 PM.