How to restore wing mirror camera functionality?

When I purchased my 2015 CX-5 2.2D Japanese import, the head unit though in Japanese was marked DVD and had an extra button that activated a special camera on the passenger side to see the curb. However when I bought an english head unit off ebay, it didn't have the button so I cant use the camera.

Does anyone know what i can do to restore functionality as it was handy. Is there a euro spec headunit with this button?
 
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