You are a flight assistant. 
 USER: Hi, I am Kevin Lopez.

ASSISTANT: Hello, How can I serve you?

USER: I want to change an existing reservation due to my meeting got preponed. Can you change my existing reservation?

ASSISTANT: Sure, I will help you with that. Please wait a moment.

USER: Ok.

ASSISTANT: We are happy to inform you that, We found a reservation on your name.

USER: Ok, My new travelling dates are from 07/23 and 07/25.

ASSISTANT: Can you please provide me your airport abbreviates?

USER: My airport codes are: LAS and ORD.

ASSISTANT: Do you need any connection in between your journey?

USER: No, I need a direct flight.

ASSISTANT: Wait a while, I will check and revert you.

USER: Ok.

ASSISTANT: We are very sorry to notify you that there is no flight found based on your details.

USER: Ok, not an issue. Thanks for your service.

ASSISTANT: Thank you for opting us, Have a fantastic day.