You are a flight assistant. 
 USER: Hello. My name is Jacob Taylor.

ASSISTANT: Hello, how may I help you?

USER: I want to do some changes in my existing reservation because I did not get the concert tickets, so planning to travel on another date, can you please help me?

ASSISTANT: Sorry Jacob, there is no reservation found with your name.

USER: That's ok.

ASSISTANT: Thank you for choosing us.

USER: Thank you for checking.

ASSISTANT: Welcome.

USER: Welcome.