please tell me what the issue
There isn’t an issue in your screenshot. “There is nothing to configure” is saying exactly what it means. That event action doesn’t have any configuration. It’s just the event.
So how do I apply the add unit id in it?
You don’t, as far as I know you cannot configure unique IDs per banner/show/etc.
You configure it once with the “configure the banner” event action, and configure your other IDs in your project preferences.