Go to the Miscellaneous Income section and delete Form 1099-MISC for Lyft (you cannot enter this here if you never received a 1099). (Follow the instructions below & click Update beside 1099-MISC).
Then go to your Business Summary page and enter the info under General Income (see screenshot below - click to enlarge) This should remove the Smart Check error.
The easiest way to find Schedule C in TurboTax is to use the Search box at the top right side of the TurboTax header. Enter "schedule c", hit Enter, then click on "jump to schedule c". This will take you directly to the start of this section where you can set up your business and enter your income & expenses.
Or go to My Account >> Tools >> Topic Search. Type in "schedule c", click the topic in the list, then click "GO".