December 2018 paycheck is showing up in January 2019 for taxes. I need this adjust prior to issuing the W2s. How do I adjust paychecks and taxes to previous month?
Probably not. Paychecks appear on payroll tax forms based on the date of the paycheck. If you paid employee for working in 2018 with a paycheck dated in 2019, then that's a 2019 payroll and is not reported on 2018 payroll tax forms.