The German AT rocket is more powerful than the US counterpart, however it only comes with two rounds. For this reason, you might choose to prioritize targeting armor, rather than enemy spawns.
The reference points for range are quite clear and defined, however, be cognizant of the unforgiving drop rate that the rockets have.
Simply ping the center or base of the desired target, line the ping up with your reference point for that range (while zoomed**) and fire away.