You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How may I assist you today?

USER: I want do some changes in my existing reservation. can you help me for that?

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

USER: Thank you.

ASSISTANT: May I know your name?

USER: My name is Sandra Hall.

ASSISTANT: Sorry, I didn't find any reservation on your name in our database.

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

ASSISTANT: Welcome, thank you for reaching us.