You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello. How can I assist you now?

USER: I am Melissa Walker. I want to change an existing reservation due to sudden change in my trip. Can you help me?

ASSISTANT: Sure Melissa Walker, I will help you with that. Please be hold on for a moment to check your reservation status.

USER: Ok.

ASSISTANT: Sorry Melissa Walker, no reservation has found under your name to change.

USER: No issue. Thank you.

ASSISTANT: Thank you for choosing us, have a good day.