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

ASSISTANT: Hello, how may I help you at this moment?

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

ASSISTANT: Sure, please wait for a minute.

USER: Ok.

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

USER: Ok, no issues. Thank you for your service.

ASSISTANT: Thank you for reaching us.