How do you make units wander around the entire map?

I was told:

Events
Time - Every 10.00 seconds of game time
Conditions
Actions
Custom script: set bj_wantDestroyGroup = true
Unit Group - Pick every unit in (Units owned by Player 12 (Brown)) and do (Actions)
Loop - Actions
Set loc = (Random point in (Playable map area))
Unit - Order (Picked unit) to Attack-Move To loc
Custom script: call RemoveLocation(udg_loc)


But i cant find where to select

" Set loc = (Random point in (Playable map area))
Unit - Order (Picked unit) to Attack-Move To loc"

Im so frustrated >.<

please help me!