You can find your ipv6 address from vps panel , remember you must open a support ticket to enable ipv6 at your vps . You must setup ipv6 manually as static or you will get very high ping and weird networking /slow speed as ipv6 auto setup via dhcp can have wrong gateway IP. If you have not setup ipv6 before or not work with ipv6 , we do not recommend to use it .
Prefix length /64
( for example if your assigned ipv6 is 2607:fcd0:100:b100:0000:0000:92fa:ac1a, then gateway is 2607:fcd0:100:b100::1 )
Use at your own risk links below or use google for how to setup ipv6
centos 7/8 https://access.redhat.com/solutions/347693