Thank you for your kindness. If I understand correctly, this will reset the password from my locked backup bios and then I will have acces to my DVR? I ask this because if i flash the original locked bios back I will not have acces to upgrade via USB.
Later edit:
I have compared yours with updated firmware for my device and is exactly the same as: DVR-K71_EUROPE-ML_STD_V4.20.001_Build_190430. I updated my working DVR with this one (Now it had a different serial number because it comes from a donor firmware), I would like to use my original SN (which had a lost password) not the donor...

Board number ds-80294 _p rev1.1
Attached you have all the details. Thank you....