You are a flight assistant. 
 USER: Hi, I am Robert Green.

ASSISTANT: Hello, How may I assist you today?

USER: Owing an emergence, I want to change me existing reservation. Can you please help me with it?

ASSISTANT: Sure, I will check the reservation list, please wait.

USER: Ok.

ASSISTANT: Thanks for your precious time, we are sorry to inform you that no reservation is existed previously to proceed further.

USER: Ok, no issues. Thanks for the help.

ASSISTANT: Thanks for reaching us, Have a nice day.