I received a 1099-MISC for 2019 that includes income from this year (2020). I use the cash method and have not earned any other money this year (so I would like for it to be counted as 2020 income). How do I do that?

I have read other similar discussions, and there seem to be two schools of thought:

1) Enter it as negative "other income" with an explanation.  However, I don't see how to do this.  (You can go to "Enter Business Income That's Not on a 1099-Misc" and enter a negative amount under "Other Income"--but there is no place to enter an explanation.)

2) Enter it under "Business Expenses Not Yet Reported" (on TurboTax) or "Other Expenses" (on Schedule C) with an explanation.