What is Winmx & what sort of device is it runnng on? Is it working in a server mode to accept incomming connections from the web? What TCP or UDP ports do you want to forward to it?
Login to the router & go to:-
Manage My Devices > Manage Advanced Settings
Click on the Windows PC in question, followed by the Port Forwarding tab.
In the new rule, give it a name then set these:-
External port 6699
Internal port 6699
Then create another using a different name & set this:-
External port 6257
Internal port 6257
Then you will need to add an inbound rule to your Windows Firewall on your PC, or the 3rd party firewall if you use one.