[Trigger] Help with attack using trigger

[Spitzer]

Currently, I'm making my hero decrease one 'mana' everytime it attacks. I used the spellbook method and inserted the 'searing arrow' spell which decreases 1 mana and disabled the spellbook. The problem now is that I can't seem to make it automatically cast. How do I fix it so that when the map starts, the 'searing arrow' is already autocast enabled?

 

[Spitzer]

Bump...someone help me pls.