Open the App Store (iOS) or Google Play Store (Android) and search for DMSS. Download and install it on your mobile device.
Connect a monitor to your Dahua DVR and log in. Go to Main Menu → Network → P2P and enable the option. Make sure it shows "Online".
Open the DMSS app → Tap the "+" icon → Choose SN/Scan → Scan the QR code shown on your DVR screen or enter the Serial Number manually.
Choose DVR/XVR when prompted. Enter your DVR's username and password (usually admin). Once verified, you can view the live feed from your cameras.