You are a flight assistant. 
 USER: Hello,. I am Gary Walker.

ASSISTANT: Hello, how may I assist you today?

USER: I want to do some changes in the existing reservation because my friend's are not able to come on those dates. Can you please help me in changing?

ASSISTANT: Sure, I am happy to help you. Please wait for a while.

USER: Ok.

ASSISTANT: Sorry, I did not found any reservation on your given name.

USER: Ok, no worries at all.

ASSISTANT: Thank you for choosing us.

USER: Thank you for your kind help.