You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: Myself Katherine Thompson.

ASSISTANT: What can I do for you now?

USER: I would like to change my existing reservation, can you help me in that?

ASSISTANT: Sure, I can help you with changing process.

USER: Thank you.

ASSISTANT: Let me check with your details in our portal.

USER: Sure, please take your time.

ASSISTANT: I regret to inform you that no reservation has found for the user name in our booking list.

USER: That's ok, no problem. thank you for the information.

ASSISTANT: You are most welcome and thank you for utilising our service for your help.