friends go to setting open SIM sitting than go to apn than add apn
name jio4G
apn. jionet
server. www.google.com
apn type. default,supl
beerer LTE
THAM SAVE SITTING
NEXT ADD APn is. ims
name. ims
apn. ims
apn type. ims
barear LTE  than save OK
go to dialpad and dial *#*#3646633*#*#
scroll left and click to cds information
than multiple son and Click to supl than start
than click ims start if that is not start turn on mobile network .
go back Engering Mode find main page this is first page find IMS click it than ussd is on and click to set than go back and click to comman find operator go in and click to volte_RJIL and set it press back go to mnncc setup and click to on press set that is process to on the volte  that is permanent setup but never switch off your phone or airplane mode. thanks