You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: I am Jonathan Lewis.

ASSISTANT: How could I assist you today?

USER: I meeting got postponed as of now , so I need to change my existing reservation. Can you please help me?

ASSISTANT: Please give me a moment.

USER: Sure, I will wait for your response.

ASSISTANT: There is no reservation found with your provided name.

USER: No problem, thank you for checking.

ASSISTANT: Thank you for choosing us.