There are two lists of cameras in the top part of the AviExport utility window.

Cameras allowable for select are presented in the left list, selected cameras for archive export  - in the right list. Select camera in the list and use  or  buttons to replace camera from one list to another

Use the  button to replace all cameras from the left list to the right list, use the  button to replace all cameras from the right list to the left list.