Change Audio input programmatically doesn't change Audio engine input AVFoundation

These are some related code segments. enableMic programmatically is the issue.

private var audioEngine: AVAudioEngine?
private var inputNode: AVAudioNode!

private func setupAudioSession() {
    do {
        let session = AVAudioSession.sharedInstance()
        try session.setCategory(.playAndRecord, options: [.defaultToSpeaker, .allowBluetooth])
        try session.setActive(true)
    } catch {
        print(error)
    }
}

func setupAudioEngine() {
    audioEngine?.stop()
    audioEngine?.reset()

    setupAudioSession()

    audioEngine = AVAudioEngine()
    inputNode = audioEngine?.inputNode

    guard let hardwareSampleRate = audioEngine?.inputNode.inputFormat(forBus: 0).sampleRate else { return }

    let format = AVAudioFormat(standardFormatWithSampleRate: hardwareSampleRate, channels: 1)

    let requiredBufferSize: AVAudioFrameCount = 4800

    inputNode.installTap(onBus: 0,
                         bufferSize: requiredBufferSize,
                         format: format
    ) { [self] (buffer: AVAudioPCMBuffer, _: AVAudioTime) in
       /* process the buffer */
    }

    audioEngine?.prepare()
}

func startRecording() {
    do {
        try audioEngine?.start()
    } catch {
        print("Could not start audioEngine: \(error)")
    }
}

private func observeRouteChanges() {
    NotificationCenter.default.addObserver(self,
                                           selector: #selector(handleRouteChange),
                                           name: AVAudioSession.routeChangeNotification,
                                           object: nil)
}

@objc func handleRouteChange(notification: Notification) {
    guard let userInfo = notification.userInfo,
          let reasonValue = userInfo[AVAudioSessionRouteChangeReasonKey] as? UInt,
          let reason = AVAudioSession.RouteChangeReason(rawValue: reasonValue) else {
        return
    }

    switch reason {

    case .newDeviceAvailable, .oldDeviceUnavailable:
       /* enableMic with current route AVAudioSession.sharedInstance().currentRoute.inputs.first */

    default: ()
    }

}

private func enableMic(mic: AVAudioSessionPortDescription?) {
    let session = AVAudioSession.sharedInstance()
    do {
        try session.setPreferredInput(mic)
        /* re-setup the audio engine and start */
    } catch {
        print(error)
    }
}