The sPoE systems should generally back up to MP4, not .264. You can’t pull the files from the HDD directly, they have to be backed up from the NVR. The NVR uses a proprietary file system.
If you are having difficulty with the password, first try the default 111111, if that doesn’t work, factory reset the NVR by pressing the pinhole in the back for 30 seconds.
Resetting the system will not erase any recordings on the HDD. It can even be done with the HDD disconnected.
Additionally, you indicated that the video is needed for legal issues, so it is likely very important that nothing on the drive is modified.