You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how can I render you today?

USER: I need to modify the travel dates in the past ticket because I am unable to travel due to some health issues. Can you please help me to do that?

ASSISTANT: Sure,I will help you with that.

USER: Thank you for accepting my request.

ASSISTANT: Let me know your name to check your reservation?

USER: My name is Mary Thomas.

ASSISTANT: Ok, please wait a moment.

USER: Ok, take your time.

ASSISTANT: Thank you for waiting. I have checked in reservation list to change your ticket, but could not find any reservation with your name.

USER: It's ok, not an issue. Thank you for your time.

ASSISTANT: Thank you for choosing us.

USER: You are welcome.