In a simple interest loan the remaining balance and interest are essentially recalculated monthly. So in the first month you will owe $10k * 7.39% / 12 = $61.58 of interest. If you pay say $200, then you'll pay $61.58 of interest and $138.42 in principal. Your new principal balance will be $9861.58, and your interest the next month will be that amount * 7.39% / 12 = $60.73 etc.

However, double check that your car loan is simple interest, because most are not. They are usually on a schedule with a fixed monthly payment, with the interest high and principal low in the first month, and the opposite in the last month.