First you need to go to device configuration menu and go to the Registrar/Video Recorder tab
Here you can configure the recorder mode, namely:
Select camera which you want to turn on to the recorder (up to 4 cameras)
Set interval of recording video in seconds (from 60 to 3600s)
Select Source RTSP stream with which the video will be transmitted (1 stream - highest quality, 2 streams - lowest quality)