Hello and welcome to the forum,
First - this is a help forum Not a do-it-for-me forum.
Second - when posting a question/problem, you need to clearly explain what you want to learn.
What have you done so far? Where are you stuck?
What does "duplicate" mean to you (account number, userid, price, the entire record, something else)? Is the file in sequence?
For requests of this type, it is best to show a small amount of input data and the output you want when your process is run. Explain any/all rules for getting from the input to the output.
Hope this helps,