Port Forwarding Wizard is a very simple port forwarding app for iPhone. Support iOS8.0 and above.
The Port Forwarding Wizard communicate with router by using UPnP or NAT-PMP standard. So what you need to do is just enable UPnP or NAT-PMP option in your router.
When you launch Port Forwarding Wizard, it will auto detect your router. When your router is detected, the tool will fetch current port forwarding entries from router and display for you.
Then you can just simply click "add" button on gui, then please fill in the port that you want to forward and internal ip address.
Anyway, It is very simple to use:)