如何通过该功能外的按钮修改功能？

func locationManager(_ manager: CLLocationManager, didUpdateLocations locations: [CLLocation]) {

    let location = locations[0]

    let kmh = String(format: "%.0f",(location.speed*3.6))
    let ms = String(format: "%.0f",(location.speed))

    speedLabel.text = kmh // change [kmh] to [ms] when the button is tapped
func locationManager(_ manager: CLLocationManag