You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: Melissa Roberts here.

ASSISTANT: How can I assist you?

USER: I need to change my existing reservation due to some issues, can you help me in changing the reservation.

ASSISTANT: Yes, I will help you. Please wait, let me check your reservation status in our database.

USER: Ok, take your time.

ASSISTANT: Sorry, I have not found any reservation under your name in our database.

USER: Ok, no issues. Thank you for the information.

ASSISTANT: You are welcome and thank you for choosing us.