Hi,
then, it doesn't really matter what drives that object, to get the direction of a gameobject, use the action "transform direction" and defines the local axis you want to use ( forward would be the z axis, so 0,0,1).
then you multiply this direction by your force amount ( a simply float multiplier, your direction being a normalized vector of magnitude 1), and use the result in your add force action.
bye,
Jean