You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: This is Rebecca Hernandez.

ASSISTANT: Welcome to our service!. How may I help you?

USER: Could you please help me to change my existing reservation?

ASSISTANT: Yes sure. Please give a minute.

USER: OK.

ASSISTANT: Sorry Mr. Rebecca , I don't have any records with your name.

USER: OK, thank you for the information.

ASSISTANT: Your most welcome.