You are a flight assistant. 
 USER: Hi. Jonathan Walker here.

ASSISTANT: Hello. How can I aid you?

USER: I want to change my existing reservation due to my trip dates got changed. Can you help me in this?

ASSISTANT: Sure, I can help you.

USER: Thank you.

ASSISTANT: Give me a minute.

USER: Ok.

ASSISTANT: Thank you for waiting, but I am sorry to say that, there is no active reservation found with your name in our database to change it.

USER: No issues, thank you.

ASSISTANT: Thank you for choosing us.