How to access data from a subarray by UI Designer?

How can I access data from a subarray in UI Designer? Following the example of expense reports that is available in Bonita Community, I was able to add the data to an array in the UI Designer and then bring them to the BonitaSoft studio, however I have a dropdown that should be filled according to item Selected in the first dropdown, according to the following image:
https://drive.google.com/file/d/0B8aMiLwwVY0nUXM5LWEwMmFvckE/view?usp=sh...

To get fill the second dropdown was using a variable REST API that brought me the content of the BDM that was with the same code selected, my API REST is like this:

../API/bdm/businessData/com.company.model.ModeloImpressoraSuprimento?q=findByCodigoModeloImpressora&p=0&c=10000&f=codigoModeloImpressora={{2}}

But there where the number "2" I do not know what I put so that it only brings me data according to the first selected dropdown

And I confirmed my array is being filled correctly from acorod with the selected item:
https://drive.google.com/file/d/0B8aMiLwwVY0nWXNHWkVjMmJ4SFk/view?usp=sh...

What I really need now is figuring out how to access the item in this array so I can fill the second dropdown correctly