Need to use jiofi for voice call

i owned iPhone 6s with iOS 11 upgraded. I was eager to use iPhone to make wifi calling using JIOFI device. But, I couldn't find the option from settings to make Wifi calling from iPhone 6s. I wanted the feature very much. But, Got disappointed without the specific feature. My primary mobile carrier is vodafone. How i can make use of JIOFI device to make wifi voice calls from my iPhone. Please suggest.