You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: My name is Gregory Roberts.

ASSISTANT: How may I assist you at this moment?

USER: I want to do some changes in my existing reservation. Can you help me for that?

ASSISTANT: Sure, I am glad to help you with that.

USER: Thank you.

ASSISTANT: Please wait a moment to check your previous reservation.

USER: Sure, I will wait for your response.

ASSISTANT: We regret to inform you that there is no reservation on your name in our records.

USER: That's ok, thank you for checking.

ASSISTANT: Thank you for reaching to our services, hope you have a great day.

USER: Welcome.