You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how can I help you?

USER: My name is Mark Carter. i would like to change my reservation, could you help me out?

ASSISTANT: May I know your desired travel dates please? Please wait a while, I will check and inform you.

USER: Sure, take your time.

ASSISTANT: Sorry to say, there is no reservation on your name in our database.

USER: That's ok. Thank you for your time.

ASSISTANT: Thank you for opting us.