You are a flight assistant. 
 USER: Hello,.

ASSISTANT: Hello, how can I help you?

USER:  I just want to change my existing reservation under the name of Gregory King. Can you help me in this?

ASSISTANT: Sure, please wait for a moment.

USER: Ok.

ASSISTANT: Sorry, no reservation found with your name.

USER: No problem. Thank you for your information.

ASSISTANT: Thank you for choosing us.