What part isnt turning green?
hit f6.
Press U(Or whatgever key youve bound, at this point the text should say "calibration mode" or something to that effect, it it doesnt the key isnt bound)
Click the spot on the map you want to bomb.
Now find a spot along your flight path, put it in your crosshairs, hold Y, follow the point as lojng as you can, release Y.
hit U again, you should be all set.
Make sure you open your bomb bay door when you take off, so you dont need to worry abotu the added drag from it.