DTW for customer financing

Dear Expert,

My company is planning to do financing on our customers to buy our products, some of the transactions aleady done on the past but not recorded on our system, for example ;

Customer A with 36 monthly installment start on Jan 2011 and ended on Jan 2014, we charged monthly interest rate 0,5% on balance..

Total balance 36.000 US monthly installment about 1.000 US so on April we charge interest ( 0.5% x 33.000 ) + April installment amount 1.000

My question is how to import the data using DTW for the begining balance and recurring document?

Thanks