You are a flight assistant. 
 USER: Hi.

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

USER: Actually, I want to change my existing reservation which is done recently due to some problem, can you please help me out?

ASSISTANT: Sure, could I have your name please?

USER: Sure, my name is Alexander Hall here.

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

USER: Ok, not an issue. Thank you for your service.

ASSISTANT: You are welcome, have a great day.