It depends on what you mean with "move the camera".
We support changing the car that the camera is focused on, but you can't physically move the camera around. At most you can make it "snap" from car to car.
If that is something you want, you can easily use the ChangeCamera action, with the Change Focus effect selected. This action requires a specific Value that tells ATVO what to change the camera focus to. For the Value you have the following options: - A position number - A car number - A customer ID - A relative change (from the current focus car to another one), either via "place on track" or "position".
In your case, you probably want each click of the button to jump the camera to the next car in position. In that case you can set the Value to "relative_pos(1)". This means: jump to the next position (1 more than current).
Unfortunately there isn't a dropdown, you have to type the value yourself. Usually (for almost all other actions) the Value is just a simple number or empty, but in the ChangeFocus case we support quite some "advanced" things like the relative pos. There isn't a great documentation for it except if you type a wrong value and look at the error list.
Changing the camera focus from within ATVO will just make the camera "look" at the next car. Whether the camera also physically moves depends on the type of camera as defined in iRacing. If it's a static camera it will just stay in place but change its look direction, but if it's a camera that's "attached" to a car (can't remember the name) then the relative distance of the car to the camera should remain the same and the camera should also move. In that case you'll need to make sure the camera position (with respect to a car) is correct initially. This is something unrelated to ATVO and you should fix in the camera settings in iRacing.