You are a flight assistant. 
 USER: Hello. I am William Anderson.

ASSISTANT: Hello, how may I be at your service today?

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

ASSISTANT: Sure, we are here to help you.

USER: Thank you.

ASSISTANT: Please wait for a while.

USER: Sure.

ASSISTANT: Sorry to inform you that, we did not find any reservation against your name.

USER: That's fine, thank you for your service.

ASSISTANT: Thank you for opting us.