There are 3 ways each for connecting to your IPv6 WAN connection:
The DHCP Client is the most straight forward of the three and this is mostly used when you’re connecting your device behind another router, all you have to do is select the DHCP Client option in the protocol drop down and you’re good to go.
If you know the IP address, gateway, network prefix and the upstream gateway doesn't support DHCP you should pick this option.