There's the event "Player - Chat Message" in the event-list. Then, as action, SetVariable and an If/Then/Else-Function (if: string comparison)
Example:
(we think player 1 types "-duel arena1)
Event: Player 1 (red) types a chat message containing -duel as A Substring
Action: Set Region1 = (Substring((Entered chat string),7,12))
<here the trigger refers to the word "arena1", region1 is a simple string variable>
2. Action: If (region1 Equal To arena1) Then (Move Unit To Region) Else (Do Nothing)
Hope you understand that, else I'll type it more detailed.