Contribution error

Hello. We have a new hire that elected Roth, but the contributions were mistakenly set to pre-tax. This only occurred on his third paycheck. I’ll be working with our 401k provider to move the funds to the Roth account, but What else do we need to do to correct this? Is a qnec necessary? 

were dollars withheld from pay as pre-tax deferrals? but they should have been withheld as Roth deferrals?

Were they withheld as Roth deferrals , but just deposited as pre-tax?

If the payroll is correct- but deposits were wrong, just as the recoredkeeper for a correction. 

If payroll was wrong- are  you going to adjust payroll records?  or are  you leaving as is?

If leaving  as is - the participant should be offerred the option for an in-plan Roth conversion, which will convert the pre-tax deferrals into Roth deferrals, and  the recordkeeper typically issues a Form 1099-R showing it as taxable to the participant. 

This is an operational error for failure to carry out the terms of the plan (i.e.,, the election of the participant).  As such self-correct by removing the contribution from the participant's pre-tax account under the plan and put it into a Roth account under the plan.  No QNEC is necessary because you simply did not put it in the right account.  (The employer had authorization to deduct the amount from their paycheck and the deduction was made.)  Then, as @justanotheradmin suggests you must take care of the taxation aspect of the contribution to ensure the Roth nature of the contribution.  The 1099-R as @justanotheradmin suggests would remove the issue of withholding and ensure its taxation but something about it seems a little distasteful as it was not the employee's fault (no election should be required for Roth treatment as it should have been a Roth from the beginning).  Since this error likely occurred recently, I would likely suggest that the employer manually correct the payroll to reflect the proper income tax withholding (that means the correction would flow through to their W-2 for the year) and contribute the missed withholding for the employee as it was the employer's fault that withholding wasn't taken (of course, the employer could request the employee pay the required withholding or withhold amounts from the employee's next paycheck to cover the withholding but, if considering getting the withholding from the employee, just issue the 1099-R).

Thank you both so much! This was very helpful. We will be self-correcting and will manually correct payroll so that it flows through their w-2 since it is a pretty recent error that was caught early. Thank you!