Nighthawk M6 MR6500 unable to port forward internal traffic to the modem's internet IP

I have a Nighthawk M6 model MR6500, Hardware version 1.0, Firmware version NTGX65_10.01.49.00, firmware build date 2022/09/09.

The internet IP for the modem is a static IP to allow me to host a web service on a connected computer.

I port-forward to the computer hosting the web service.

External traffic to the internet IP (static IP) address is successfully port-forwarded.

Internal traffic to the internet IP (static IP) address goes to the modem/router (192.168.1.1).

How can I configure this router to port forward internal traffic to the Internet IP to my computer hosting the web service?