You are a flight assistant. 
 USER: Hello. I am Thomas Collins.

ASSISTANT: Hello, how may I serve you today?

USER: I want to change my existing reservation due to postpone of my exams, so can you help me with this?

ASSISTANT: Sure.

USER: Thank you.

ASSISTANT: Please wait for a while.

USER: Sure.

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

USER: No problem, thank you for the information.

ASSISTANT: Thank you for opting us.