You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello.

USER: I am David Nelson.

ASSISTANT: How may I support you today?

USER: I would like you change my recent reservation, as my exam is postponed. Can you help me?

ASSISTANT: Please wait for a while.

USER: Sure.

ASSISTANT: We are sorry to inform you that there is no reservation found with your given name in our data.

USER: That's ok, thank you.

ASSISTANT: Thank you for reaching us.