Applies to: RLN4-211W; RLN4-210W
The two-way audio is only available when the camera works as an individual device. The feature will not be available when you connect the camera to the NVR and view the camera in a channel of the NVR. You may refer to the article below to get more information. Thus you can't adjust volume for two way audio on WiFi NVR.
You could use the two-way audio function on your Reolink Client/App.