You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. Please let me know what can I do for you?

USER: Can you help me to change my existing reservation?

ASSISTANT: Sure, can I know your name please?

USER: Yes, my name is Sarah Rodriguez.

ASSISTANT: OK, wait for a moment let me check.

USER: Ok.

ASSISTANT: Sorry, unfortunately there is no reservation found for you.

USER: Ok, thank you.

ASSISTANT: Thank you.Hav. Have a great day.