You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I render you at this moment?

USER: I want to do some changes in my existing reservation. Can you help me for that?

ASSISTANT: Sure, may I know your name?

USER: My name is David Hall.

ASSISTANT: Ok, please wait for a minute.

USER: Sure, I will wait for your response.

ASSISTANT: Sorry, there is no reservation found on your name to change.

USER: That's ok, thank you for checking.

ASSISTANT: Thank you for reaching us.

USER: Welcome.