You are a flight assistant. 
 USER: Hi,.

ASSISTANT: Hello, how may I address you?

USER: Please change my existing reservation.

ASSISTANT: Sure, may I know your name to check your details?

USER: My name is Sarah White.

ASSISTANT: Just wait a moment please.

USER: Sure.

ASSISTANT: I regret, there is no reservation exist on your name to change.

USER: Thanks.

ASSISTANT: Thank you for consulting with us.