You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how can I assist you?

USER: I want to change my existing reservation which is done recently due to some problems, can you please help me in this?

ASSISTANT: Sure, I am here to help you. May I know your name?

USER: Sure, my name is Donna Hernandez.

ASSISTANT: I am sorry to say you that there is no reservation found under your name in our database.

USER: Ok, no problem. Anyways, thank you for your service.

ASSISTANT: Thank you for choosing us.