Where on TurboTax do I indicate what dollar amount of dividends are section 199A dividends?

Section 199A dividends should be shown in box 5 of your Form 1099-DIV. On the screen in TurboTax where you enter the 1099-DIV, check the box that says "My form has info in more than just these boxes." Then enter the amount in box 5.

See the following FAQ for instructions to enter your Form 1099-DIV in TurboTax Online.

Where do I enter my 1099-DIV in TurboTax Online?