First of all: Your device needs to support VoLTE.
Second: Your device needs to have the correct information stored into the firmware (by the device manufacturer).
Third: Your contract needs to have VoLTE support.
In case one is not met, you won't be able to use VoLTE.
And there is no manual on how to enable VoLTE - as this is either supported out-of-the-box -OR- there are device-specific routines needed. Especially for devices not sold by Vodafone, this can be nearly impossible to cover.
