Inseego FX2000-3 unable to access from internet to local network

I recently acquired an Inseego FX2000-3. From this I can access the Internet using the LAN and Wi-Fi but I need to be able to access (rdesktop) from the Internet to a computer on the LAN, how can I do it?
I tried ippasstrough connecting directly (point to point) the PC to Inseego and it didn't work and when I try to do port forwarding, port 3389 is not valid.
I need to know how I can access a computer on my LAN from the Internet? Saludos