UPDATE: As well as still not being able to change the icon, I have found out that I cannot change some of the settings too. For instance, I tried to click the 'Is mobile enabled' button to the unticked position, but I can still play the game on my iPad or other devices!!! Any ideas anyone???
EDIT: This is getting even weirder: now the icon has updated when I log onto my phone and search for it, but it still has not updated when I look on my computer...