You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello,. How can I help you?

USER: I have a request to change my existing reservation.Can you please help me in changing?

ASSISTANT: Sure, may I know your name?

USER: Dennis Garcia is my name.

ASSISTANT: Please wait a minute. I will check and inform you.

USER: OK.

ASSISTANT: Thanks for waiting, sorry to say that no reservation is found regarding your details.

USER: OK, thanks for your information.

ASSISTANT: Thank you, for contacting us. Have a nice day.