ohh and you must use an runnable class to update the coordinates because that arrow is static showing the given coords not the target. if you want ofc. :) btw good job! (kinda late but who cares :D)
Forgot to say, first use removeAllMarkers for your own good, don't wanna get your player with millions of markers :P
player.getRadar().removeAllMarkers();
or you can keep track of the coords given and remove only the marker like that:
player.getRadar().removeMarker(x,y,z); (don't know why i'm saying that sure you already know that staff ) :D