You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: My name is Christine Walker.

ASSISTANT: Walker, how may I aid you today?

USER: I want to do some changes in my existing reservation. Can you help me for that?

ASSISTANT: Sure, I am here to help you. Hold on for a moment. Let me check.

USER: Thank you. I will wait for your response.

ASSISTANT: Sorry Walker, there are no flights reserved on your given name.

USER: That's ok, thank you for checking.

ASSISTANT: Welcome, thank you for choosing us. Have a great day.

USER: Welcome.