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

ASSISTANT: Hello, How can I serve you?

USER: Owing to an emergency, my meeting with client got postponed. So I request you to change my existing reservation.

ASSISTANT: Sure, Please wait a second.

USER: Sure.

ASSISTANT: Sorry, No reservation found on your name.

USER: Ok, not an issue. Thank you for your assistance.

ASSISTANT: Thank you for opting us.