Hey Andrew,
In your ball Blueprint, you can reference a specific actor in your level. Create a new Actor Variable and make it Editable, then Compile. In your level, select Blueprint and go to Details panel. There will be a new section named Default with your new Variable in it. In drop down, select your Trigger Box.
Now in your Blueprint, drag your Variable into Event Graph and select Get. That’s your reference to specific Trigger Box you wanted. rest is simple: create an Event Actor Begin Overlap node, then link that to a Branch node. Drag off Other Actor pin and type == to get a comparison node, to which you can attach your Variable referencing Trigger Box.
What this is doing is checking to see if your ball is overlapping with something, and if it is, whether it is overlapping your Trigger Box. If that’s true, you can then drag off True pin of Branch node. In picture above, I am simply printing “Contact”, but yours can certainly do something more complex.
Hope that helps!