You can add under the /etc/config/network file, configure as follows,
config interface ‘wan6_4’
option proto ‘464xlat’
option ip6prefix ‘dd50:e735:b42d:1111::/96’
and then execute cmd: /etc/init.d/network restart
Option ip6prefix is just an example. This is the ipv6 prefix of a NAT64 server. It is usually provided by the operator. You can ask the operator.