You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how can I help you?

USER: I am Melissa Hall. I would like to change my existing reservation because my sister marriage was postponed, can you help me?

ASSISTANT: Sure, I am here to help you. Please wait, let me check your reservation status in our database.

USER: Sure, take your own time.

ASSISTANT: Sorry, I did not find any reservation under your name in our database.

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

ASSISTANT: You are welcome and thank you for contacting us.