Payslips that are already approved by the Finance department can be reverted (With the status 'approved') to 'Pending' status from the Payroll module at any time. 

To revert the payroll,

1.  Navigate to ERP > Human Resource > Payroll

2.  Filter the employees by the desired filters.

3.  In the generated employee list, click on the Revert button to revert the payslip.