How to use bp 'aimoveto' in a actor which hasn't been created?

I tried to build a tower that can hit the actor which close the tower by creating an arrow flying towards to the actor to cause damage,but it didn’t work.So I tried to build an arrow in the scene to test bp"aimoveto",I found it really did work. So I think the problem is the bp “spawnactor”,but I don’t know how to solve the problem,so I come here to ask the question to search for someone can help me solve the problem. My English is not very good,so the pic is better.