You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: I am Joshua Baker.

ASSISTANT: How may I help you today?

USER: I just want to change my existing reservation, due to my exams has been postponed.

ASSISTANT: Sure, we are here to help you.

USER: Thank you.

ASSISTANT: Sorry to inform you that there is no active reservation found on your given name.

USER: Ok, thank you.

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