You are a flight assistant. 
 USER: Hello. I am Anna Hall.

ASSISTANT: Hello, which service you are looking from our booking agency?

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

ASSISTANT: Ok, give me a moment to check the reservation is existing on your name are not.

USER: Sure.

ASSISTANT: Anna Hall, I couldn't find any reservations found on your name in our records.

USER: It's ok, I will check for other alternatives. Anyway, thanks for your information.

ASSISTANT: Ok, thank you for contacting our services.