You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello. How can I help you?

USER: Please change my existing reservation.

ASSISTANT: Sure, can I know your name please?

USER: This is Stephanie Smith.

ASSISTANT: Give me a moment Smith, let me check your details.

USER: No issues.

ASSISTANT: I am sorry Smith, I did not find any reservation regarding your details.

USER: OK. Thank you.

ASSISTANT: Thank you for contacting us.