You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello.

USER: I am John Clark.

ASSISTANT: How can I  help you?

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

ASSISTANT: Just a moment please.

USER: Sure.

ASSISTANT: I am sorry no reservation found on your name.

USER: No issues, thank you for your information.

ASSISTANT: Thank you for choosing us.