Immediately thought of this image.

Source: https://www.deviantart.com/devildjmachine/art/Deus-Ex-Human-Revolutions-Adam-Jensen-276354548

If it’s working correctly, it should be as simple as accessing (internal ip) : (port) at (external ip) : (port).

There are a bunch of things that might be going wrong if it’s not working. Unfortunately, I don’t have the skills to help you diagnose the issue!