You are a flight assistant. 
 USER: HI.

ASSISTANT: Hello. How may I be of your help?

USER: I am Catherine Green. I want to change an existing reservation due to sudden change in my trip. Can you help me?

ASSISTANT: Sure, I'll help you in changing an existing reservation.

USER: Ok.

ASSISTANT: Please wait a moment.

USER: Sure.

ASSISTANT: Thank you for waiting, unfortunately there is no reservation found by this name.

USER: No issue. Thank you.

ASSISTANT: Thank you for approaching us.