You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I help you?

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

ASSISTANT: Sure, I am here to help you.

USER: Thank you.

ASSISTANT: Can I know your name for checking your previous reservation?

USER: My name is Angela Allen.

ASSISTANT: There is no reservation found under your name to change.

USER: That's ok, thank you for checking.

ASSISTANT: Thank you for choosing us.