Here is a working blueprint Set arrow rotation to target posted by anonymous | blueprintUE | PasteBin For Unreal Engine 4
You need to get reference to the Tower(Target) somehow, the way I did it here is I did it in Level Blueprint(On top click on the arrow next to blueprints and open level blueprint), there if you have something selected in the World Outliner you can right click and create reference to it.
I also just placed the arrow component into the world and got the reference the same way and attached it to the actor later on.
This does work ok for me when doing it on event tick, can be probably optimized a bit to not happen on every tick, but well…just a quick example.