You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How may I help you?

USER: I would like to change my existing reservation, can you help me in that?

ASSISTANT: Yes, can you tell me your name?

USER: Myself Mark Thomas.

ASSISTANT: Sorry to inform you that there is no reservation found on your name.

USER: That's ok, no problem. Thank you for the information.

ASSISTANT: Thank you for contacting us.