I had to find out a script for something simmilar this is prehaps all that you need.
enemyaa2 DoTarget blackhawk2
~3
enemyaa2 Fire [AALauncher, AALauncher]
But change "enemyaa2" to the units name of your unit with the RPG. and change "blackhawk2" to the name of the unit that will be targeted by the RPG soldier.
But also you will need to change
[AALauncher, AALauncher]
To the name of the "weapon & ammo used" Such as
weapon used ==>[RPGLauncher, RPGLauncher
RPGLauncher] ammunition used.