Hello. Myself Jennifer Collins.
user
Hello, how may I serve you at this moment?
assistant
I want to change my existing reservation, can you help me in that?
user
Sure, I will help you. Please wait for a moment.
assistant
Sure, I will wait for your response.
user
Sorry, there is no reservation existing on  your name.
assistant
That's ok, no problem. Thank you for the information.
user
You are welcome, thank you for reaching us. Have a nice day.
assistant