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

ASSISTANT: Hello, how may I help you at this moment?

USER: Due to an emergency in my friend's home, I would like to change my reservation.

ASSISTANT: Sure, please let me check your ticket details in our database.

USER: Ok, take your time.

ASSISTANT: Sorry, there is no ticket existing in our database under your given name.

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

ASSISTANT: Thank you for reaching us.

USER: Welcome.