It depends on what you want it to look like, if it is an arrow like on a minimap than having it as a UMG widget is the solution and that is sadly something I have never done.
If you want to have it like an arrow above the characters head(or in front of it or whatever) than having it as an actor in game is the way and that is what I sent you.
You should have all the information you need at your disposal now, you know how to get the direction to the target using my BP(you can convert this into a vector, by breaking it and making a vector), you can get your character current rotation using what NoobsDeSroobs told you in the other reply. And you can calculate the angle between the two to set the render transform of the UMG widget(Hint:
).
Try to move from here on your own, experiment a bit, best way to learn to be honest.