You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: I am Dennis Lewis.

ASSISTANT: How can I help you Dennis?

USER: I  want to change my reservation due to my office work was scheduled on the same day, so help me on that?

ASSISTANT: Oh! that's sad, let me go back and check with your previous booking.

USER: Ok.

ASSISTANT: Dennis Lewis, there is no reservation by your name. Sorry for the inconvenience.Can I help you with any other information, let me know?

USER: Oh! that's my bad luck, any way thank you for your help.

ASSISTANT: That's great of you, keep reaching us for your bookings in future as well.

USER: No thanks, I am ok with this.

ASSISTANT: You are welcome.

USER: Ok , thank you.