The iCap software is designed to control several types of cameras including NexImage 5. Not all cameras use all features of the software. The NexImage 5 does not have a built-in iris, focuser, or zoom mechanism, so these features cannot be accessed.
You can adjust the zoom for the view on the screen using the magnification, however this only changes the screen display and isn't zooming the camera. This is helpful if you are shooting at full resolution where you will only have a fraction of your image displayed on your monitor. It lets you zoom out to see the whole image on your screen.
The zoom setting does not affect what the camera is capturing. You won't be able to fit the entire lunar disk on the chip with longer focal length telescopes.
The only way to do capture such a large object is to reduce the focal length of the scope or your image capturing setup. Try a focal reducer or removing any Barlows or eyepiece projection you might be using.