welcome to the forums, Sax!

to answer your question:
at the start of the skirmish, the mount triggers and exerts enquea. then, during a skirmish the freepeoples player has the first action: in this case heal enquea to make
hrethel strength +3. now you as the shadow player get the next action: if enquea is already healed and no wound on it is left, you cannot heal him anymore.
it's always the same: the freepeople player takes the first action.