If you are using the TurboTax Deluxe desktop program on your computer, simply open the program and select your return from the list. If you haven't filed the return, you can make edits as needed. If you have already filed then return, you can select to amend, or if the return was rejected you can correct the return and re-file.
If you don't see them under Continuing Your 2018 Tax Return, you may also select Find a Tax File.