You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello. How may I aid you?

USER: I want to change my reservation due to health problem, can you help me?

ASSISTANT: Sure, I will help you with that.

USER: Thank you.

ASSISTANT: May I know your name to check your reservation status.

USER: Myself David Martinez.

ASSISTANT: Sorry, there is no reservation found on your name in our records.

USER: No problem, thanks for checking.

ASSISTANT: Welcome.