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

ASSISTANT: Hello, how can I help you?

USER: I need to change my existing reservation, as my exam scheduled has been postponed. Please help me in cancelling?

ASSISTANT: Sure, please wait for a while.

USER: Ok.

ASSISTANT: Sorry, no reservation found on your given name.

USER: Ok, no issues.

ASSISTANT: Thank you for choosing us.

USER: Thank you for your help.