Your internal IP address (LAN) is probably different than the default IP address of the Dahua OEM cams. The default IP address for Dahua cams is 192.168.1.108.
The easiest way is to take a laptop or computer (if it has an ethernet port) or a tower and turn off wifi and connect the camera cable to the laptop (obviously you need power so if it is on a POE switch then connect a cable from the switch to the computer).
Then go into ethernet settings and manually change the IP address of the laptop to 192.168.1.100.
Then go to a browser and type in 192.168.1.108 (default IP address of Dahua cameras) and you will then access the camera.
Then change the camera to the IP address range of your home network (using the IPv4 settings), but have the last digits something not already assigned.
Then go back into ethernet settings and change the computer IP address back to what it was previously (probably DHCP)
Then replug in everything like it was and proceed from there.
Or download Dahua toolbox and run the batch config tool where you can Initialize the camera and change it's IP, but most of us do what I mentioned above as we do not like our cameras touching the internet.