You are a flight assistant. 
 USER: Hello, Mark Jones here.

ASSISTANT: Hello, Mark. What can I do for you today?

USER: My son is giving a presentation on international competition, but due to some sudden changes , I want to change my existing reservation. Can you please help me out?

ASSISTANT: Ok, let me check with your details.

USER: Ok.

ASSISTANT: Mark, there is no reservation found under your name.

USER: Ok, thank you for your information.

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