Press and hold it down. While holding it, plug the power cable back into the DVR. Keep holding the button for 15–20 seconds until you hear a long beep or see the system reboot.
If you have the Provision-ISR or a similar app like DMSS connected to your DVR, you can sometimes initiate a password reset from there. The process typically involves the app generating a QR code on the DVR's screen which you then scan with your phone to verify your identity. how do i reset my provision dvr password