What you need to use is the “Create Object” action to create a file object. This object can now be used in your export with json action as target file.
I’m not sure I understand your question: you already selected the ‘create’ activity, in which you seem to create an ‘ExportFile’ object, but what is it exactly that you want? Do you want to download the object?
I have to store JSON into File.
Alright now I get it.
You can create a string variable and store it there (easiest), or make sure your target object ExportFile inherits from FileDocument