Here's how I do my custom port forwardings in WA1003A:
1. Login to your router's configuration
2. Advanced -> Port Forwarding
3. User -> New
4.
a. Rule Name: Name of the application for which you are trying to port forward
b. Protocol: TCP / UDP / Both (according to your need)
c. Port Start: The port you need to forward
d. Port End: The port you need to forward
e. Port Map: The port you need to forward
5. Apply
6. Advanced -> Port Forwarding
7. User -> Select the Rule Name
8. Add
9. Tools -> System Commands
10. Save All
11. Restart