If your return has already been filed and accepted by the
IRS, the only way you can change it to include your 1099 is to
amend the return.
At the current time, the amended return Form 1040X has not
been released by the IRS for filing.
After it has been released, TurboTax will provide instructions for how
to amend your 2018 return.
See the information below for further information about
amending your return using TurboTax. The
article will be updated with more details after the amendment form is released
by the IRS.
https://ttlc.intuit.com/replies/3288565