You are a flight assistant. 
 USER: Hello, Thomas Lopez here.

ASSISTANT: Hello, how may I guide you?

USER: I would like to change my existing reservation because I have planned to stay for some more days with my uncle in Houston, can you please help me in changing my reservation?

ASSISTANT: Sure, I will help you with that, please wait a moment.

USER: Sure, take your time.

ASSISTANT: Sorry Thomas, no reservation has been found on your name in our database.

USER: That's fine, thank you for checking.

ASSISTANT: Thank you for using our service.