You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello, what can I do for you today?

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, may I know your name please?

USER: Sure, my name is Donald Hill.

ASSISTANT: Sorry, no reservation found on your given name in our database to change it.

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

ASSISTANT: Thank you for contacting us.