Get your taxes done using TurboTax

first you should check code section 7872 to see if it applies and if it does do you need to report imputed interest, it also gives some directions on how to compute it. 

https://www.law.cornell.edu/uscode/text/26/7872 

if you do need to report 

use the interest and dividends section in Turbotax. use the interest on 1099 link. click on add investments and skip import. click on the interest icon and continue. skip the FEIN box enter the borrowers name and the interest on line1