Re-fueling is covered in Lesson VI of the Tutorial sessions. I have not checked out the ones that were issued with the game, but the sessions were re-written for the PlayersDB and I know that they work.
Grab the Complete Harpoon ANW Library [PlayersDB-7.4.7-ANW]
and unzip this file to your "Databases" sub-folder normally found at:
C:\Matrix Games\Harpoon 3 Advanced Naval Warfare\Databases
When you start up the Harpoon3 ANW Launcher, select the PlayersDB and then load Lesson VI of the Tutorial set of scenarios.
You can get a point-by-point description about how to use enable aerial refueling by selecting "PC" from the Menu Bar at top left hand corner of the screen and then selecting "Original Harpoon2 Tutorial".
Good luck to you and post up if you have further questions.