You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: I am Thomas Campbell.

ASSISTANT: Thomas, how may I help you?

USER: I am planning to change an existing reservation, due to health issue. Can you please change my reservation?

ASSISTANT: Sure, I can help you. Please hold on for a moment.

USER: Sure.

ASSISTANT: Sorry, no reservation is available by your name.

USER: That's fine. Thank you for your service.

ASSISTANT: Thank you for reaching us.