Give your units a variable that signifies whether they have moved or not (or use one that they already have like action points etc). For simplicity lets use a boolean, "Ready".
When you go to pick a enemy unit to move you use these events :
Pick all - Enemies (pick all is from the system menu)
Enemy is Ready (get this from the enemy object itself, comparing boolean)
Pick a random instance of Enemy (from the system menu again)
The above picks all enemies for you to select from,
Then only selects those that are ready,
Then refines it a single random one that is ready.
Now that you have 1 unit selected you can run your chain of functions.