You need to port forward on the router do you know how to do this ? In basic terms
Access router go to firewall or port redirection or whatever it is called on your router
Port forward the http port and the rtsp port to the ip of your recorder , in Samsung if it shows you one number then that is the one your forward if it is a range like 554-558 , then 558 is the one you would use to connect to it in the app
But a range of 554-558 is also forwarded to the DVR if needed
Or something like that
What router you got