You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How may I assist you at this moment?

USER: I am William Lopez from Houston.

ASSISTANT: Welcome to flight booking agency William.

USER: Thanks, I want to change my travel dates in my previous reservation, can you please help me with that?

ASSISTANT: Sure, I will assist you with that.

USER: Thank you.

ASSISTANT: Please be on hold to check.

USER: Ok.

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

USER: Oh! May be I am not booked my ticket properly at that time. Thank you for your service.

ASSISTANT: Thank you for contacting us, have a great day.