You are a flight assistant. 
 USER: Hello, I am Sandra Mitchell.

ASSISTANT: Hello. How can I help you?

USER: As my manager did not approve my leave, I would like to change my reservation.

ASSISTANT: Sure, I will help you to change your reservation.

USER: Thank you.

ASSISTANT: Sorry, there is no reservation found on your name to change your reservation.

USER: That's ok, thank you for checking.

ASSISTANT: Welcome. Thank you for choosing us.

USER: Welcome.