Your app name is not "app", it's something like "cmd shortcut" :-) It most likely has several icons, scattered across several folders, each used for a different thing.

OK here's a bone for you. I've downloaded the deb file and looked at the contents. You icons are:

/usr/share/icons/hicolor/48x48/apps/cmd-shortcuts.png
/usr/share/icons/hicolor/scalable/apps/cmd-shortcuts.png

They are both the same visually, only different sized. Why don't you copy them to your PC and edit them, or create completely new ones and overwrite the originals?