Hi !
You will need to send an email request for reset password to HikVision tech support by usind SADPtool for generating xml file info of the DVR and send it to them so they can provide you a key to reset the password .
(you need to keep the dvr connected to the internet and you shouldn't power off the device.)
If you could make a dump of the Bios and send it to me i could help you with resetting it . (It requres soldering skill and you need a SPI Flash Reader to do it.)