icom OS supports port forwarding. Create a port forwarding rule as outlined below:
Add under Network → Firewall / NAT a new Destination NAT rule.
Configure as Type Portforward, your desired Protocol, the Input interface und last your desired IP address and Port number.
If your firewall is active, add under Network → Firewall / NAT a new IP filter rule and select FORWARD as Packet direction and the Protocol, configure your Input and Output interface. It is very important here to set your Destination port and enter the IP address with a Subnet mask of /32.
A comprehensive configuration example can be found in this Configuration Guide.