Forgetting passwords can be a pain in the bum, but its a bigger pain if you don't know how to reset the Dahua password.
Instructions below:
https://dahuawiki.com/PasswordReset
If you've not selected an email recovery option and security questions were not selected, please follow these instructions instead
First Step - Download config tool (if you don't have it already) - https://dahuawiki.com/ConfigTool
