Edit the file eth0 (or similar) config file,
If your network interface isn't eth0, you can find it by checking,
and then editing that config, replacing NETWORK_INTERFACE with the correct network interface,
And then add the following to the end of the file,
IPV6INIT=yes IPV6ADDR="IPv6_RANGE/NETMASK" IPV6_AUTOCONF=yes
Information for the IPv6_RANGE/NETMASK can be found from CrownPanel.
Save the file and then,
systemctl restart network