There is actually nothing to fix.
Wages are attributed to and report in the year (and the reporting period) they are paid, not when they're earned.
So, your December payroll, paid in January 2020, is reported on 2020 forms: Reported on the Q1 2020 941 and state quarterly forms and on the 2020 W-2.
They're also they're included in the YTD numbers on pay stubs, to match government reporting.