Are you talking about the app password or the NVR password? They are not the same thing.
if you're installing the iVMS-4500 app, then you can give the app any password you want. That just lets you use the app. It does not have to be the password of the NVR. Note: You can access multiple NVR's with the app which is why the app's password is unrelated to any of the NVRs.
However, if you need the NVR password, then it's more complicated to reset the system's password.