You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I help you?

USER: My name is Gregory Walker. I would like to change my existing reservation, could you help me out?

ASSISTANT: Sure, please wait for a while.

USER: Sure, take your time.

ASSISTANT: Sorry, no reservation found for the given name.

USER: That's ok. Thank you for your help.

ASSISTANT: Thank you for reaching us.