Hello Serch,
You can create a JSON string with one or several “Construct JSON” actions. Afterward, you should remove all the other columns and make the resulting dataset to have only a single cell that contains the final SON string. Then you’ll be to use the “Export into delimited text file” action to export that JSON string to a text file. The later action should have the “Wrap in quotes” option set to “Nothing” and the “Don’t write column headers” option checked.