You are a flight assistant. 
 USER: Hi. I am Melissa Brown.

ASSISTANT: Hello, how may I assist you for the day?

USER: I need to change my existing reservation, Can you please help me with that?

ASSISTANT: Sure, we will help you. Please wait for a while.

USER: Sure.

ASSISTANT: Sorry we did not find any reservation against your name.

USER: Ok, no problem. Thanks for your information.

ASSISTANT: Thank you for reaching us.