If the door is locked using one of the Touchscreen 2n Security Panels that look like this:
If you are using a Nelson Brothers 2n Security Card, tap your Card to the device.
If you are using the My2N Mobile app on your phone, first tap the screen.
You should then see the bluetooth unlock icon in the bottom-right corner.
Press and swipe the icon to the left side of the screen and release.
The device should give an audible alert and the device will show a green banner at the top saying "Door open" indicating the door has been unlocked.