Set file to 'upload free' in the csv file

-- HikaShop version -- : 2.3.1
-- Joomla version -- : 3.3.1
-- PHP version -- : 5.4.12
-- Browser(s) name and version -- : Chrome

Hi, how to spécify a file as "free upload" in a csv file.
I can't find a field to set up this value.

eg:
product_name,product_code,categories,product_parent_id,Format,price_value,images,files,???
_MG_2150.JPG,_MG_2150.JPG,,,10cm x 15cm,,_MG_2150.JPG,_MG_2150.JPG, Here the free upload flag !
......
thanks for your reply