You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello, how may I help you?

USER: Can you help me to change my existing reservation?

ASSISTANT: Sure, may I know your good name please?

USER: Stephen Allen here.

ASSISTANT: Ok, please wait for a while.

USER: Sure.

ASSISTANT: Sorry to say that, there was no reservation found with your given name.

USER: Ok, no problem. Thank you.

ASSISTANT: Ok, thank you for opting us.