Help Move Camera in front of actor

Hello everybody, i am trying to solve a problem over a week now doing (re)search all over the places without any results.
The problem i have is that i got a spring arm with a camera attached at a length (pawn without character) and position is 0,0,0. There is an actor located at a position allways closer to the world center as the camera. Now i would like to rotate the spring arm to have the actor in front of the camera, better saying in the middle of my view. I could not figure out how to calculate the distance or which direction i do have to rotate the spring arm to accomplish this, any help will be so much appreciated.

For completeness here the solution