You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello,. How may I assist you?

USER: I would like to change my existing reservation which was made on the name of Melissa Davis. Can you help me update my reservation?

ASSISTANT: Please wait for a while.

USER: Sure.

ASSISTANT: I regret, no reservation found by name Melissa Davis.

USER: That's ok, thank you for the response.

ASSISTANT: Thank you.