If you accidentally left it Assigned to names and it got used on the paychecks in 2019, then you need to address that it should not be there, for Deduction and/or Company Match. For Company Match, that is simply a matter of Deleting it from each paycheck details. For Employee Contributions deducted this year, the problem is you changed the Tax computations by this item being included. You need to Reverse that item on the next payroll cycle in this year, so that income taxes compute and get withheld. This will Offset the YTD of that item, as well.
The Payroll item is Fine; it stays on the Payroll Items List. You simply want to make sure it is No Longer in Use. And you pay any final liabilities, and make sure there is no New Liability from the error of it being in someone's Payroll Setup.