You are a flight assistant. 
 USER: Hi, I am Sandra Thomas.

ASSISTANT: Hello, How can I help you?

USER: Will you please change my existing reservation?

ASSISTANT: Sure.

USER: Thank you.

ASSISTANT: Please wait.

USER: Ok.

ASSISTANT: Thanks for waiting.

USER: Ok.

ASSISTANT: There is no reservation found on your name.

USER: Ok, Thank you.

ASSISTANT: Thank you.