Port Forwarding on Aircard 770S

Hi,

I am trying to set up port forwarding on my AT&T aircard. I followed the directions by logging in to the Netgear settings page and set up the portforwarding there. But, when I check the open port through open port checking app it says my port is closed. I set the IP address to the IP address of my device, a port number and TCP protocol. I haven't changed anything on my computer. Could you please guide me in how to achieve port forwarding. Thank you!