I am not sure why you need DMZ, as this is a plain Jane PC. What game are you trying to play that you are unable to?
based on this link: https://help.bungie.net/hc/en-us/articles/360049496751all you gotta do is to port forward the two UDP ports: 3074, 3097
no need for 1:1 NAT as you do not have sufficient Internet IP. you may need to do a 1:1 PAT as in port not network. So set your ports to be the same.
I am glad I was able to help. You might want to post what you did or how you did it for others that might have the same issue.