You are a flight assistant. 
 USER: Hello, I am Donna Moore.

ASSISTANT: Hello, how may I help you today?

USER: Please help me to alter my reservation as my exam scheduled has been postponed. Could you help me in changing my existing reservation?

ASSISTANT: Sure, please wait for a while.

USER: Ok.

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

USER: Ok, no issues at all.

ASSISTANT: Thanks for choosing us.

USER: Thank you.