If it was reported on 1099-DIV it may be handled in the Free Edition. (There are some unstated limitations on the TurboTax website.) Please check under Interest and Dividends if it will take. If it will not, try just adding the capital gains to the ordinary dividend (box 1) and leaving the capital gains blank. If this doesn't increase your tax or only by a tiny amount, I, personally, would do that and if the IRS sends a letter inquiring about it, just tell them what you did. They are quite happy to have you pay more tax than necessary. I'd hate to have you spend something like $50 to report $40 of income.
Otherwise, assuming you have an otherwise simple return, you might consider reentering the information in one of the other IRS FreeFile options available at
https://www.irs.gov/filing/free-file-do-your-federal-taxes-for-free
I know some of them do handle capital gains in their free edition. You should check on their state filing limits, too.