How do I access the same WordPress page from WAN and LAN?

I've got a WordPress installation over LAMP on a Raspberry Pi 3B+ (a small Linux-based board). All fine from local, so I decided to extend it worldwide. I have put the Raspberry Pi on DMZ of the router and changed ports from 80 to 8080 (port 80 is reserved for the router) and got a DDNS from No-IP, because my router supports auto-updates with NO-IP. I can access fine with WAN (when I'm not on my own network), but I can't when I'm in my OWN network. I type the ddns, but it redirects me to local IP, and wordpress only accepts through the DDNS link. I need help so I can access from both links.

I expect that I can access from both links, but I can only access from one, which is the external one.