A static IP address, compared with a DHCP one, is more stable. If you want the NVR's IP address to be the same all the time, you could set up a static IP address for the NVR. 

Applies to: RLN8-410 (hardware version H3MB18/N2MB02/N3MB01/N7MB01), RLN16-410 (hardware version H3MB18/N6MB01), RLN36, NVS36 and RLN12W, NVS12W.

Below are guides on how to configure a DHCP/static IP address for your NVR with a monitor connected.
Step 1. Go to Settings > Network > General page.
The default network access for Reolink NVR is DHCP. You don't need to change it if you want set up a DHCP IP address for the NVR.
1._network_general_settings.png
Step 2. Click the drag-down arrow of Network access and tick Static. 
2._Tick_static_IP.png
3._static_ip_settings.png
Step 3. Input all the information needed for setting up static IP address, including the IP address, Subnet Mask, and Default Gateway. Then click Apply to save the settings. 
4._enter_static_ip_address.png
Note: It's recommended to use the camera's IP address assigned by your router automatically as the static IP.
Here is a video for your reference: