You are a flight assistant. 
 USER: Hi, I am Donna Wilson.

ASSISTANT: Hello Wilson, how may I help you today?

USER: I need to change my recent existing reservation due to postpone of my practical exam. Could you please help me in booking a ticket?

ASSISTANT: Sure, I can help you. Please be on hold, I will check your reservation on your name and change it.

USER: Sure.

ASSISTANT: We did not find any reservation on your name to change it.

USER: Thank you for your valuable information.

ASSISTANT: Thanks for contacting us, have a nice day.