You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I help you today?

USER: I am Timothy Hernandez. I want to do some changes in the existing reservation because my friends are not able to come on the those dates, can you please help me with that?

ASSISTANT: Sure, I will help you.

USER: Thank you.

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

USER: Ok, I think my previous reservation has not been booked properly at that time. Thank you for your information.

ASSISTANT: Welcome, have a nice day.