Terrafoming
As we know Neptune is a gas giant, which means that the planet is all gas. To make it look like and be like Earth first you will need to drain all the gasses, ices, and liquids off leaving only the core and enough water and other materials to provide oceans and an atmosphere. Then you add salt to the oceans, and begin transplanting life, while fertilizing and using techniques to create soil. You then add a moon for permanent plate tectonics, water cycle, and axial tilt support.