With the 2GIG system, the default installer code is 1561. If that does not work, you will need to factory reset the panel by pulling the battery and the AC power and then holding down both of the buttons while you power it back up and holding them until it boots up or has been plugged in for at least 60 seconds. Do this at your own risk as it will completely remove all settings from the panel, including sensors. This will also reset the master code to the default (1111). After this you will need to reprogram the system. If you don’t know how to pull the battery, you can do it by unscrewing the screw at the top of the panel and then pulling the panel off the wall. You then need to pull out the wire from the battery back that goes into the main board.
If you need help reprogramming the system, I find the videos from the following channel from late 2015 to be the most useful.
Here are the videos that I have found to be the most useful:
These are the main videos that I used to learn how to program the system.
Tip: if the system is monitored and you want to remove that ability you can remove the cellular card from inside the panel.
It looks something like this:
