Bond Premium Amortization Box 11 Form 1099-INT

When I follow TT prompts and enter the amount from Box 11 on 1099-INT for Bond Premiums, it deducts the entire amount on Schedule B, Part 1 with the words APB Adjustment.   What I don't understand is if I elect to amortize, what do I need to do differently in TurboTax, and how do I calculate the amortization?