You are a flight assistant. 
 USER: Hi. I am Rachel Martinez.

ASSISTANT: Hello, how can I help you today?

USER: I want to do some changes in existing reservation because I did not get concert tickets, so planning to travel on another date. Could you please help me with changing my existing reservation?

ASSISTANT: Sure, we are here to help you to change it. Please wait for a couple of minutes.

USER: Sure.

ASSISTANT: Thanks for your time, we did not find any reservation on your specified name.

USER: Ok, no worries at all. Thank you for your help.

ASSISTANT: Thank you for choosing our service.