Adobesign | How to fetch/set custom fields of a Template from Adobesign Templates API

We have been trying to fetch and set the method/api through which we can fetch custom fields of a Template but unfortunately we haven't found any end-point. 
Can someone help us or guide us how we can fetch/set custom fields of a Template from Adobesign Templates API ?

Adobesign has done something similar while making their App for Salesforce using custom templates option: https://helpx.adobe.com/sign/using/salesforce-data-mapping-templates.html

But, in their API documentation, there is no end-point to fetch or set fields: https://secure.na1.adobesign.com/public/docs/restapi/v6

Help would be much appreciated!

Best Regards