How to enable VoLTE in Samsung Galaxy S7 in india...?
Samsung Galaxy s7 is an LTE device and not VoLTE. But if you still want to make voice calls over LTE, you can download jio 4G voice app from https://www.jio.com/en-in/apps/jio-4g-voice  . 

It is very user friendly app,still in its beta phase. But it lets you enjoy all the features of VoLTE while you are in LTE.