ViewController.swift

var audioEnabled = true

@IBAction func toggleMic(sender: AnyObject) {
    agoraKit.muteLocalAudioStream(audioEnabled)
    audioEnabled = !audioEnabled
    // Update the button title
    if (audioEnabled) {
        self.micButton.setTitle("Mute", for: .normal)
    } else {
        self.micButton.setTitle("Unmute", for: .normal)
    }
}