I don't know how long ago you played but all you have to do is get a general lineup with your target then press F6 this will enter you in calibration mode. Press U then hold down Y for some time but make sure not to long or you will miss your target, 10 seconds is about right. Set your salvo's line up perfectly with your target and drop the bombs.
Im not the best at bombing but im sure someone will post a link to the HTC Trainers website and that will also help.