You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello.

USER: I am Dennis lopez.

ASSISTANT: How can I render you at this moment?

USER: I need to change my existing reservation, Can you please help me with that?

ASSISTANT: Sure, I will help you.

USER: Thank you.

ASSISTANT: Please wait let me check the current status.

USER: Sure.

ASSISTANT: Sorry  Dennis Lopez, no reservation found on your name in our data base.

USER: Ok, no problem. Thanks for your information.

ASSISTANT: Thank you for contacting us.