Using T-rex dataset with OpenNMT

I’m a student and i’m learning the basics of NLP.
I find OpenNMT a very intresting tool and i’m trying to understand it, after i’ve completed a couples of tutorial i’m trying to understand how to use OpenNMT for Data to text tasks.
I completed webNLG challenge 2017 (WebNLG Challenge 2017 - WebNLG Challenges) using OpenNMT-py and now i’m trying to follow the same pipline using the t-rex dataset(T-REx : A Large Scale Alignment of Natural Language with Knowledge Base Triples).
However i don’t understand how can i obtain the src and tgt files from the NIF or JSON file of t-rex dataset.
Is there a documentation about this step? How can i use T-rex dataset with OpenNMT-py?
Thanks for your attention