If you did not include all your income, you will need to file an amended return including your overlooked income with the IRS and your state, if you are required to file a state return.
You will need to use a form called 1040-X, which can be prepared for free in TurboTax. You cannot e-file an amended return. A 1040X has to be mailed, and it takes 2-4 months for the IRS to process an amended return.
You
cannot generally file an amended return until after your return has
been processed by the IRS and you have received your original refund
(if any). This is because the IRS often catches
errors during processing and will correct them. If you owe money to the
IRS after calculating your amended return, you should mail your amendment to be
postmarked before midnight, April 17, 2018, to avoid penalties and
interest.
Here are the instructions to Amend
My Return