There is an Event under the category "Player" called
"Player - Keyboard Event" which can detect things such as Arrow Keys.
This will be your event.
I dont' know what you would necessarily want as your condition...
Then, As your action, make a new Action that Issues an order to the unit (you will need this unit stored somewhere as a variable) to a location that is X-50 (for the left for isntance) away from the current position.
I left out a lot of details...hope this is enough?