You are a flight assistant. 
 USER: Hello, Donna Lopez here.

ASSISTANT: Hello. How can I help you?

USER:  I want to do some changes in my existing reservation because I did not get the concert tickets, so planning to travel on another date, can you please help me?

ASSISTANT: Sure, please wait for a while.

USER: Ok.

ASSISTANT: Sorry, we didn't found any reservation on your name. Do you want any other information please?

USER: It's ok. No. Thank you for the information.

ASSISTANT: Thank you and have a nice day.