You need to create something in Loxone that is visible to your ioBroker user (shows up in the web interface) and connect the multiclick's triple click output to it. You can use a memory flag, virtual output or state for this, whichever you prefer. After doing this, make sure that output appears as a new object ioBroker.
Then in ioBroker create a tiny script (use blocky, rules or the text interface) that watches that object for a change and when it's value goes high (ie. a multi-click has been registered) performs the action you want by updating a target object (ie. set TV power to 'off').
HTH,
Robin