Capital gain distributions are reported on Form 1099-DIV, in box 2a. Click Wages & Income, then click "I'll choose what I work on." On the screen "Your 2019 Income Summary," scroll down to the "Interest and Dividends" section. Click the Start or Update button for "Dividends on 1099-DIV."
But you mentioned Schedule D. Do you have to correct capital gains from investment sales, not capital gain distributions? If so, scroll down to "Investment Income" (just below "Interest and Dividends"), and click the Start or Update button for "Stocks, Mutual Funds, Bonds, Other."
