(new problem ) need your little help please

[omniversal]

i put an ability called Autofrostnova to an item that every times the the hero attack (must use right click to targeted unit ) it will cast frost nova. my question is : how to use a GUI trigger to make the autofrostnova ability which on the item to dealt damage 30x of hero strengh every time i attack (autofrostnova will autocast when i attack an enemy ) ???

note : not the item dealt damage 30x of hero strengh but the autofrostnova ability. For this i put an example map. if you dont understand what i mean please PM me or post here