If the NVR still supports the Hikvision
tftp updater method of applying firmware, implicit in this method is a reset to default settings, which will clear the presumed corrupted database and replace with a clean default template.
For the Hikvision tftp updater you will need :
The updater itself downloaded from the 'custom downgrader' second link here :
Custom Firmware Downgrader 5.3.0 Chinese to 5.2.5 English
The same firmware file you already used to update with.
The PC wired (not WiFi) with an IP address of 192.0.0.128
Start the tftpserve.exe program, click OK to the Windows firewall query, check the status window shows 'initialised' on 192.0.0.128
Power on the NVR and observe the status in the tftp updater window.
You may have to power cycle more than once.
If / when it shows 'Update successful', shut down the tftp updater.
Activate the NVR via SADP.
Good luck!
If that does not 'take' - it's easy enough to do the update via the serial console, given the serial TTL to USB convertor, and the right connector.