You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: My name is William Turner.

ASSISTANT: How can I assist you?

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

ASSISTANT: Sure William, give me a minute.

USER: OK.

ASSISTANT: Sorry, there is no reservation found with your details.

USER: OK, thank you for your information.

ASSISTANT: Thank you.