trigger for computer hero leveling

[Biggs]

In my map, when a player leaves, all units are given to the computer. I'm not using any AI, but I want the heroes to level up their skills when the computer has them. I made a trigger that when a unit levels up (owned by comp) as the event and then for the action I put down learn skill for every hero skill in the map, this does not work. so I was wondering if anyone knows how to make that work with triggers?

just a note: it seems that gang wars fans love my map from when i tried advertising it as like gang wars, which was part of the inspiration.