You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I assist you today?

USER: Actually my friend decided to change the trip dates, because he was unable to travel on the dates he planned,  so can you help me to change his existing reservation?

ASSISTANT: Sure, I can help you with that. May I know your name to check the previous reservation?

USER: My friend's name is John Green.

ASSISTANT: John, I see that there is no reservation found under your name.

USER: It's ok, thank you for the information.

ASSISTANT: You are welcome. Thank you for contacting us.