You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, what can I do for you today?

USER: I need to change my reservation as my plan to go for trekking got postponed. Can you help me?

ASSISTANT: Sure, I am here to help you.

USER: Thank you.

ASSISTANT: Can you mention your name to check further in our database?

USER: I am Dennis Mitchell.

ASSISTANT: Please stand by.

USER: Sure.

ASSISTANT:  Sorry, no reservation found with your given name in our database to change it.

USER: Ok fine, thanks for your response.

ASSISTANT: Thank you for contacting us and have a nice day.