extension UIApplication {

    // If false, alternate icons are not supported for the current process.
    @available(iOS 10.3, *)
    open var supportsAlternateIcons: Bool { get }


    // Pass `nil` to use the primary application icon. The completion handler will be invoked asynchronously on an arbitrary background queue; be sure to dispatch back to the main queue before doing any further UI work.
    @available(iOS 10.3, *)
    open func setAlternateIconName(_ alternateIconName: String?, completionHandler: ((Error?) -> Swift.Void)? = nil)


    // If `nil`, the primary application icon is being used.
    @available(iOS 10.3, *)
    open var alternateIconName: String? { get }
}

import UIKit

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
    }

    @IBAction func didTapChangeIcon(_ sender: UIButton) {

        // Info.plist で設定した値
        let iconName = "facebook Icon"

        UIApplication.shared.setAlternateIconName(iconName) { error in
            if let error = error {
                print(error.localizedDescription)
            }
            print("Done!")
        }
    }
}