what to do for VOLTE in India's jio network?
If you want to flash a new ROM then you should collect essential information from XDA forums about your device. Flashing a new ROM is a risky task so you must create a backup or something to fix your handset.

If you don't want to risk anything then use Jio4GVoice https://play.google.com/store/apps/details?id=com.jio.join&amp;hl=en . You can Call, SMS, etc without a VoLTE enabled handset.