Can someone tell me how to add existing cameras to my panel?
What kind of cameras are you referencing?
If you are referencing Alarm.com video cameras, they do not connect through the alarm panel. They are connected through your internet to Alarm.com.
You will need a service plan which supports Alarm.com video. You can add video support at any time in the system manager here.
Afterward, steps to add an Alarm.com video device to your account can be found here.
You can then choose to stream compatible cameras on your IQ Panel screen.