I use zorin lite , so I have menu editor(menulibre) by default, I have done that before with programs located in places other than the downloads or desktop locations and that place the link on my super menu in zorin lite, but I don't try that with app.sh
I think u just need to add path field under exec field in your .desktop(path=/home/mech-one/Downloads/songkong), but if that not worked , u can try the gui way