PORT Forwarding with Panoramic (TG1682) model does not work

Tried with wifi.cox.com and 1+ hours with cox care tech and get errors on the web site trying to add/delete/edit.  Also can't change on the modem directly DHCP to Reserved IP.  I've read a few threads from it can't be done to connect device to wifi first and do it, then connect back to ethernet and it should work, but none works for  me,