You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello.

USER: Rebecca Wilson here.

ASSISTANT: How may I guide you today?

USER: Can you change my flight ticket reservation?

ASSISTANT: Sure, I will help you with that. Can you please wait for a while.

USER: Sure.

ASSISTANT: I am sorry to say that there is no reservation.

USER: Not a problem. Thank you.

ASSISTANT: Thank you for contacting us.