You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello, do you need any help from us?

USER: I want to change my existing reservation which is done recently because of postpone of my examination, can you please help me in this?

ASSISTANT: I understand your request and will be happy to help you.

USER: Thank you.

ASSISTANT: Could I have your name please?

USER: Sure, my name is Joseph Martin.

ASSISTANT: Sorry, there is no reservation matching with your name in our portal to make changes further.

USER: Ok, no problem. Anyways, thank you for your service.

ASSISTANT: My pleasure. If any questions arise, please feel free to contact us at any time.

USER: Definitely, thank you.