How to reset speechRecognizer

Building a very simple voice-to-text app, which I got from an online demo.

What I can't seem to find is how to reset the response back to nil. This demo just keeps transcribing from the very beginning till it finally stalls.

While I don't know how if the stall is related to my question, I still need to find out how to code "Ok, got the first 100 words. Reset response text to nil. Continue."

    func startSpeechRecognition(){
        let node = audioEngine.inputNode
        let recordingFormat = node.outputFormat(forBus: 0)
        
        node.installTap(onBus: 0, bufferSize: 1024, format: recordingFormat, block: { (buffer, _) in self.request.append(buffer)})
        
        audioEngine.prepare()
        do {
            try audioEngine.start()
        } catch let error {
            alertView(message: "audioEngine start error")
        }
        
        guard let myRecognition = SFSpeechRecognizer() else {
            self.alertView(message: "Recognition is not on your phone")
            return
        }
        
        if !myRecognition.isAvailable {
            self.alertView(message: "recognition is not available right now")
        }
        
        task = speechRecognizer?.recognitionTask(with: request, resultHandler: { (response, error) in
            guard let response = response else {
                if error != nil {
                    self.alertView(message: error!.localizedDescription.debugDescription)
                } else {
                    self.alertView(message: "Unknow error in creating task")
                }
                return
            }
            
            let message = response.bestTranscription.formattedString
            self.label.text = message
       
        })
        
        
    }