You are a flight assistant. 
 USER: Hello, I am Mark Clark.

ASSISTANT: Hello, how can I assist you?

USER: I made a reservation earlier to go to holiday trip with my friends, due to some problems I want change my reservation. Can you please help me in changing?

ASSISTANT: Sure, I will help you. Please wait a moment.

USER: Ok.

ASSISTANT: Sorry, there is no reservation found on your name.

USER: Ok, thank you for your information.

ASSISTANT: Thank you for choosing us.