You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how can I aid you for today?

USER: Myself John Davis. Due to some urgent work, I am going to change my existing reservation. Can you please help me for this?

ASSISTANT: I am here to help you about that John Davis.

USER: Ok, I will wait for your response.

ASSISTANT: I have found your reservation. Can you please provide your modified dates of journey?

USER: I am planning my trip on Nov 19, and again I will return back on Nov 21.

ASSISTANT: Can you please provide me the respective airport codes for your journey?

USER: My airport codes are ORD to DTW?

ASSISTANT: Do you have any other requirements about your journey?

USER: My return time is evening.

ASSISTANT: Sorry to say this John Davis, there are no flights which travels on your route.

USER: Not a big deal, anyhow thank you very much for your service.

ASSISTANT: You are welcome, thank you for reaching us.