Can't say for sure on your model, but on my old Q-See QT8516 there is no PWD CLR/reset button on the mainboard, so I had to remove the CMOS/NVRAM 3v lithium battery, wait few minutes, then reinstall battery. POWER OFF and UNPLUG NVR first! You'll need to remove multiple screws holding the case cover to the lower main unit. Do this only if humid enough to prevent static, or preferably wear antistatic wrist strap. Do NOT touch sensitive electronic circuits after walking on carpet. The Q-See NVR is pretty tough, but you never know when static discharge will damage components.
Removing the battery will reset all battery backed config parameters back to uninitialized state, so you'll need to go through setup process again. Some NVRs have a reset or password clear button on the main board, but others do not (at least what I've seen). Here's what the Q_See QT8516 main board looks like, with the 2032 3V CMOS battery circled. Yours may be different. Just my 2 cents. I don't know any back door hacks to get in the Q-See NVRs, but there are probably some. Since they're out of business (in the USA), not likely to find much info on them now. Good luck.
