Once you've filed your return, the only way to add additional information would be to file an amended return (1040X), which you can do in TurboTax. But you'll need to wait until IRS has processed your original return and issued any refund. Then you can prepare the 1040X and add any missing info.
IRS only accepts amended returns on paper, so you'll print, sign, and mail it.
Here's a link to the TurboTax support page for amending returns, which will get you started: https://turbotax.intuit.com/tax-tools/tax-tips/IRS-Tax-Return/Amending-Your-Income-Tax-Return/INF120...
