When using controls in the assets panel, they are optimized for iPhone 7, so when using them on a iPhone 7 Plus
art board do they need resizing in some proportion ? such as buttons, navigation tabs ?
I checked in with one of our designers, and it turns out the difference between iPhone 7 and 7+ is screen real estate and not the size of any of the elements. So you can think of it this way: you generally don't scale the icons; you can just have more icons due to the increased height/width of the artboard.
Hope that helps!