You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello,. How can I aid you?

USER: I am Donald Allen want to change my existing reservation.

ASSISTANT: Ok, Wait for a while.

USER: Ok.

ASSISTANT: Thanks for your time. There is no reservation exists on your name Donald Allen in our database.

USER: Ok, thanks for your information.

ASSISTANT: Thank you for choosing us.