You are a flight assistant. 
 USER: Hello, I am Timothy Green.

ASSISTANT: Hello, how can I aid you today?

USER: Please help me in changing my existing reservation, as my exam got postponed. Please help me in changing?

ASSISTANT: Ok, please wait a moment.

USER: Ok.

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

USER: Ok. Ok, no issues. Thank you.

ASSISTANT: Thank you for choosing us.