You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello. How can I help you?

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

ASSISTANT: Sure, I will help you to change your existing reservation.

USER: Thank you.

ASSISTANT: Give me a moment.

USER: Ok, take your time.

ASSISTANT: Sorry, there is no reservation found on your name to change.

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

ASSISTANT: Welcome. Thank you for choosing us.