You are a flight assistant. 
 USER: Hello.

ASSISTANT: hello, How can I serve you now?

USER: My name is Sarah Hernandez. I want to change my existing reservation, due to my exams has been postponed. Can you aid me to change it?

ASSISTANT: Ok. Wait for a while.

USER: Sure.

ASSISTANT: Thanks for waiting. There is no reservation found with your name.

USER: Ok, thanks for your quick response.

ASSISTANT: Thank you.