Hello,
For what you are describing, you can go to option Network > Firewall > Traffic Rules to configure a forward rule from WAN to LAN and specify the ports, like you can see on the following wikipage:
RUT955 Firewall - Teltonika Networks Wiki (teltonika-networks.com)
It is recommended to know the specific IP address of your LAN host, not just the link-local. Could you share a topology diagram to understand what you are trying to accomplish here?
Kind regards.