You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I assist you?

USER: Please see is there any chance to change my existing reservation, as I am having a meeting with my client on the same date which is more important for me.

ASSISTANT: Sure, I will help you to change your existing reservation. On which name you reservation has been booked?

USER: Sharon Parker.

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

USER: That's fine. Thank you for your information.

ASSISTANT: Welcome. Thank you for choosing us.