NLU Inbox / Training from custom frontend


I’m using a custom frontend for my rasa chatbot (access via POST/GET to Rasa endpoints). One problem is that Rasa seems to not import any utterances into the NLU inbox so I’m unable to further classify or improve my training data. I was able to export the “tracker” database dump, but there seems to be no way of importing / converting these data into Rasa training format, does it?

Thanks and kind regards.