braicc

Hello everyone I need help in resetting my NVR. I bought from someone it look like new with all accessories in box.the model is SEN-F4120S4P Wich in Dahua site doesn't exist.It seems that is DHI-NVR4204-P when it started time was always reset to 0 and found that the battery was faulty.i have tray all the password variant non of the work. I understand that is a hidden jumper on main board for hard reset but I don't know we're is it. Thank in advance.