You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hi. How may I assist you today?

USER: I want to change my existing reservation, due to some health issue. Can you help me?

ASSISTANT: Sure, may I know your name for the changing process?

USER: Sure, my name is David Martinez.

ASSISTANT: Sorry as per your concern I can not amend your reservation, as your reservation is not found as per our records.

USER: Ok, not an problem. Thank you for your information.

ASSISTANT: Welcome, thank you for reaching us.