You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello.

USER: Myself Andrew Allen.

ASSISTANT: Nice to meet you Allen. In which way I can help you today?

USER: Due to some changes in my trip, I want to change my existing reservation.

ASSISTANT: Sure, I will help you with that. Please be hold on for a moment, I will check the existing details.

USER: Ok.

ASSISTANT: Thank you for waiting. Sorry Allen, there is no reservation has found under your name.

USER: No issue.

ASSISTANT: Thank you for reaching us.

USER: Thank you.

ASSISTANT: You are welcome.