If you want to set the NVR to overwrite the old files when the HDD is full via a web browser check the guides below.

Applies to: Reolink NVRs 

Step 1. Log into your NVRs via Web Browser, then go to Device Settings > Record page.

record_page_web.png

Step 2. Click the Overwrite option, and choose the overwrite interval based on your need. (The overwrite interval is only available to the new Hw No. H3MB18/N2MB02/N3MB01/N5MN01/N6MB01/N7MB01)

record_option_web.png