You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How may I help you?

USER:  I am John Clark want to change my reservation due to prepone of my meeting.

ASSISTANT: Ok.

USER:   Can you help me in changing?

ASSISTANT: Sure. Please wait.

USER: Ok.

ASSISTANT: Thanks for waiting. There is no reservation found on your name.

USER: Thank you for your help.

ASSISTANT: Thank you.