You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello. How may I assist you today?

USER: I need to change my existing reservation, Can you please help me with thatr?

ASSISTANT: Sure, can you mention your name for checking purpose?

USER: Ryan Jackson here.

ASSISTANT: Sorry Ryan Jackson, there is no reservation found under your name.

USER: Ok, no problem.\. Thanks for your information.

ASSISTANT: Thank you for using our service.