The account is the "master key." Without it, you cannot change network ports, add cameras, or perform firmware updates.
Locate the small silver coin-cell battery (usually a CR2032). Removing this for about 2–5 minutes and then reinserting it can often reset the system clock and, in some models, revert the password to the factory default.
If the physical reset button is broken or missing, you may need to re-flash the firmware.
H.264 DVR Password Reset Guide - CCTV & Güvenlik Sistemleri