You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I assist you at this moment?

USER: I am trying to change my recent reservation because my health is not good, so I am unable to catch the flight. Can you help me in changing the ticket?

ASSISTANT: Sure, I will help you with that. Can I have your good name for checking an existence of reservation?

USER: My past ticket is reserved with name Dennis Campbell.

ASSISTANT: Ok Dennis, please wait a moment.

USER: Ok, take your time.

ASSISTANT: Thank you for waiting. Sorry Dennis, there is no reservation found under your name.

USER: It's ok, thank you for checking.

ASSISTANT: My pleasure. Thank you for choosing us.