Hello,.
Hello, how may I abet you today?
I want to change my existing reservation due to some issues, can you please help me with that?
Sure, we are here to help you. Please wait for a moment, I will check the reservation on your name and revert to you.
Sure.
Thank you for waiting, I hardly  tried to find a reservation but there is no reservation found on your name,.
Ok, no issues. Thanks for your information.
May I know your good name to recheck your reservation?