If you cannot use the QR code method, a factory default via the motherboard is the most effective approach.
Look for two small solder pads on the motherboard labeled J1, TP, or RESET . They are often near the battery or the main processor. 7004t-lm-v3 password reset
Remove the screws on the side and back to slide the cover off. If you cannot use the QR code method,
If a standard hardware reset fails to clear the password, the device firmware may be unresponsive. Advanced users can attempt to access the bootloader interface to clear settings. 7004t-lm-v3 password reset
If no reset jumper is visible, removing the internal battery can sometimes clear the system clock and trigger a reset on older firmware: How to Reset DVR Password