Every device which is connected to router, including computer, smart phone, DVR, NVR, IP camera, no matter by ethenet cable or by wifi, will be distributed a IP by router.
All these devices are listed in router's page. Here is method to find it.
Find your router's address. Usually, router's address is as same as your computer's gateway.
1. Access router by its IP on your computer browser. The default user name and password of your router is on the label of router.
Please notice router's user name and password is not as same as wifi's user name and password.
You can also search your router's default user name and password on google.
2. Find the DHCP list. Picture below is my router's page. Every router's page is different.
3. Finally, your computer can access DVR by its IP