In what terms you are talking about?
Humanly xx simple, get hold of an eye surgeon xx cut a hole put in n an eyeball at the forehead.
Talk only, read all books of third eye ,it explain what's third eye in all styles and patterns.
Spiritually, it takes time xx years, just to know third eye, not doing it or learning about it. To have it or not, you'll not be talking here now
Any person who does or really had third eye won't be writing or talking here now.
Bless the person who had third eye and talking about it. 5555555