Corrections must always be dealt with on the basis of 'follow the money'.

This means that if an employee has been underpaid in a previous pay period, the correction of the underpayment should be made in the next payroll run you perform.
Likewise, if an employee has been overpaid in a previous pay period, the correction to recoup this overpayment should be made in the next payroll run you perform.

Where an employee, however, has physically received a payment amount in a particular pay period which differs to the amount shown in the payroll and the associated PSR has already been submitted, this will require a 'correction submission' to be made to Revenue in order to rectify the error. 

This correction submission is known as a Correction PSR.

After making a correction, where the software detects that a correction submission is required, a Correction PSR will automatically be created for you, which you will be prompted to submit.