You can open a port and/or port forward on Mushroom by adding inbound rules on the firewall tab.
Under the FIREWALL tab, click on Add Firewall Rule in the Inbound section and add the required firewall rules.
For example, the attached screenshots are to map the inbound TCP port 9091 to TCP port 8081 and directed to an IP: 192.168.251.120. And to map UDP port 5060 incoming on WAN2 to a different host located at 192.168.251.100.