You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how can I aid you?

USER: I want to change my existing reservation due to postpone of my trip with my friends, can you help me in changing the existing reservation?

ASSISTANT: Sure, could please provide your name?

USER: My name is Jacob Robinson.

ASSISTANT: OK, thanks for giving details. Please wait for a while I will check the details and revert to you.

USER: Sure.

ASSISTANT: Thanks for waiting. There is no reservation found with your specification's.

USER: Ok, not a problem. Thank you.

ASSISTANT: Thank you for contacting us.