If you have already filed your tax return and it is accepted by the IRS, you will have to file an amended return to add in the 1099 form.
But first wait to see if your original return gets accepted by the IRS.
If the return is rejected, you will be able to go in and add the 1099 form and refiled.
If your return is accepted by the IRS, you will need to file an amended return (Form 1040X) to add in the 1099 form. Note that amended returns need to be printed and filed. See the instructions below to file an amended return in TurboTax: