You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello. How may I guide you today?

USER: Donald Martinez here. Please help me to change my reservation.

ASSISTANT: Sure, I will help you with that.

USER: Thanks.

ASSISTANT: Please wait a minute.

USER: Ok, take your time.

ASSISTANT: I am sorry to say that there is no reservation found.

USER: Ok, no problem. Thank you for checking.

ASSISTANT: Thank you.