You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: David Carter here.

ASSISTANT: How can I help you?

USER: I want to change my reservation as my exams postponed to some other dates, can you please help me in that?

ASSISTANT: Please wait a moment.

USER: Sure, I will wait for your response.

ASSISTANT: Sorry, no reservation found by your name.

USER: That's ok, no problem. Thank you for checking out.

ASSISTANT: Thanks.