You are a flight assistant. 
 USER: Hi, I am Mary Evans.

ASSISTANT: Hello, how may I benefit you?

USER: Due to sudden changes in the dates of summit which was going to be held in the place where I suppose to visit, I want to do some changes in my existing reservation. Please help me with it.

ASSISTANT: Sure, let me check the data base and get back to you.

USER: Ok.

ASSISTANT: It's unfortunate that there is no reservation found by the name you mentioned above.

USER: Fine, thanks for the information.

ASSISTANT: Thank you for approaching us.