help with dmz fix for 5038f error - stuck on last part

Im following the instructions on this post but am stuck on the last part

https://www.reddit.com/r/MonsterHunterWorld/comments/805ylt/getting_5038fmw1_error_on_connection_attempts/?st=JEOQAWNM&sh=ed132da2https://www.reddit.com/r/MonsterHunterWorld/comments/805ylt/getting_5038fmw1_error_on_connection_attempts/?st=JEOQAWNM&sh=ed132da2

I have a Motorola nvg510 router and not sure exactly where DMZ is. I have read its called IP passthrough on this modem. I found that part but am unsure exactly where to put the IP address i gave it. Does anyone know?