I bond interest, paid interest on previous years. not all the interest. How do I reduce the reported interest by what I paid?

I assume you are asking about  cashed US Savings bonds (USSB). After entering the 1099-INT,  reporting the interest in box 3, you will be asked if you previously reported the interest.  Answer yes and enter the amount.  TurboTax will show the adjustment (deduction) on Schedule B