You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I help you?

USER: I am Sandra Gonzalez. I want to change an existing reservation, can you please help me in that?

ASSISTANT: Sure, please wait a minute.

USER: Sure.

ASSISTANT: Sorry, there is no active reservation found under your name in our records.

USER: That's ok, not a problem. Thanks for your information.

ASSISTANT: Most welcome.