You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: I am Melissa Walker.

ASSISTANT: Walker, how can I aid you today?

USER: Suddenly I got a call from my manager to attend a meeting on same departure date, so I need to change my existing reservation. Can you please help me?

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

USER: Ok, I will wait for your response.

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

USER: That's ok, no problem. Thank you for your information.

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