Unable to use the edit functionality of contacts using CNContactViewController in swift

Question

I am working with ContactUI in swift.I am listing the contacts using this code

    let contactPickerViewController = CNContactPickerViewController()
    contactPickerViewController.delegate = self
    present(contactPickerViewController, animated: true, completion: nil)

When i select a specific screen, the screen with details of selected contact pops up. But the "Edit" option is not available on this screen. Now I want to know how to activate the built-in edit functionality in this case.