Here's what you do:
After you enter your 1099-MISC, TurboTax will ask if you have
any other additional income. Say yes. If you have already entered your 1099 and
are coming back to the interview, just choose the second radio button "Additional income and other
income...."
Then enter an explanation such as "Income reported on 2017
Form 1099 but received in 2018" and enter as a negative number. (The minus sign goes in
front, or the software will complain at you.)
This will correct your income and let the IRS know why you're
doing it.
