Try
configure set service dns forwarding options address=/plex.local/192.168.3.4 commit save exit
Note: this will translate ANY hostname ending in plex.local to 192.168.3.4
Try
configure set service dns forwarding options address=/plex.local/192.168.3.4 commit save exit
Note: this will translate ANY hostname ending in plex.local to 192.168.3.4