Short answer is to read the manual they have a section on port forwarding. It is pretty standard you type in the ip address of the internal machine and the ports you want forwarded to that machine.
Bad news is it will likely not work. It is actually very rare to get a actual routable IP address on a LTE based system. You need to check the wan setting and see if you are getting a address out of the private blocks or you have a real public routable IP. When they use private blocks it means they have a router doing NAT between you and the actual routable IP you are using. This means to make what you want work the ISP would also have to have port forwarding....which of course they will never do.
The only way I have see people get...