You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: Myself Helen Nelson.

ASSISTANT: How may I assist you today?

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

ASSISTANT: Please wait a moment, let me check with your details.

USER: Ok, I will wait for your response.

ASSISTANT: Sorry, there are no active reservations on your name to change.

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

ASSISTANT: Thank you for reaching our service.

USER: You are welcome.