Open the web interface of the router by typing its IP address into the address bar of your webbrowser (I think it should be 192.168.1.1).
Login (The default user should be admin and the default password 1234, but I hope you have changed that )
Click on Advanced Setup, NAT, Virtual Servers
Select "custom Server" and enter 20595 for External Port start, External port end, Internal port start and internal port end and select UDP as protocol
As Server IP Address you need to enter your computer's IP address. That should be something like 192.168.1.x. On Windows open a CMD window and type ipconfig to get your IP address.
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