You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how can I help you?

USER: I want to make some changes in my previous booking, Can you please help me for changing my existing reservation?

ASSISTANT: Sure, can I ask you for your name?

USER: Sure, I am Matthew Garcia.

ASSISTANT: Give me a moment.

USER: Ok.

ASSISTANT: Sorry to inform that there is no reservation by the name Matthew Garcia.

USER: Ok, Thank you for your help.

ASSISTANT: Thank you for reaching us.