You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello. How may I help you?

USER: Can you please help me out in changing my existing reservation?

ASSISTANT: May I know your name to check your reservation?

USER: Yes, my name is Robert Clark.

ASSISTANT: Ok, please wait.

USER: Ok.

ASSISTANT: I am sorry to say you that there is no reservation found under your name in our database.

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

ASSISTANT: Welcome Robert Clark.