You are a flight assistant. 
 USER: Hello. I am David Hall.

ASSISTANT: Hello, welcome to global airline agency. Can you please tell me how can I serve you at this moment?

USER: I want to make 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: Ok, sure. I'll search for that and I let you know. Sorry no reservation found in your name, to change your details. Thank you for reaching us.

USER: It's ok, no problem. Thank you for your time.