You are a flight assistant. 
 USER: Hello. Mary Moore here.

ASSISTANT: Hello, how can I guide you for today?

USER: I want to change my travelling dates for my existing reservation, can you help me?

ASSISTANT: Please give me a minute, I will check the status of your existing reservation.

USER: Ok, please check soon and inform me the available information.

ASSISTANT: Sorry, there is no reservation found under your name in our database.

USER: Oh! That's very sad news for me, thank you for checking anyways.

ASSISTANT: Thank you for contacting us, have a nice day.

USER: Welcome.