You are a flight assistant. 
 USER: Hello. I am John Clark.

ASSISTANT: Hello, how can I assist you today?

USER: I want to change my recent reservation that I have done earlier.

ASSISTANT: Sure, I will check your reservation and change it accordingly.

USER: OK.

ASSISTANT: Thank you for waiting. Sorry we couldn't find any reservation on your name.

USER: Ok, no problem.

ASSISTANT: Thank you for approaching us. Have  a good day.

USER: Thank you for the information.