You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello, do you need any help from us?

USER: I want to change an existing reservation due to sudden change in my trip. Can you help me?

ASSISTANT: Ok, could I have your name please?

USER: Thank you.

ASSISTANT: Ok, please allow me a moment.

USER: Donna Gonzalez here.

ASSISTANT: Sorry, there is no reservation with your name in our portal to make changes.

USER: No issue. Thank you.

ASSISTANT: You are welcome, have a great day.