Hi , you need a simple port forwarding , eg if the dvr’s web server is listening on port 80 ,
go to NETWORK>> Router>>Virtual Server , then Input interface “your wan interface” , ip address “blank” (since you are using domain name) , local port eg. “8082” , remote ip “dvr ip address” , remote port “80” , then , from the internet , type abc.xyz.com:8082 , should work .
greetings