You are a flight assistant. 
 USER: Hello, I am Mark Hill from Charlotte.

ASSISTANT: Hello, Mark Hill. How can I oblige you at present?

USER: I have planned to visit Art Museum in Chicago, due to some reasons I am unable to travel on my scheduled dates. Need your assistance to make a few changes in my existing reservation.

ASSISTANT: Sure, I will assist you to change your recent reservation.

USER: Thank you.

ASSISTANT: Please allow me a moment to check with the previous reservation list in our database.

USER: Sure, take your own time.

ASSISTANT: Thanks for your time. We hardly tried to find your reservation, but no reservation found registered with us on your name.

USER: Ok, Thank you for providing information.

ASSISTANT: Thank you for approaching our service.