You can reverse a leave pay-off using the pay-off utility in the Employee section.
First, make sure that the employee you will be reversing the pay-off for is uncalculated. Delete their calculation and be sure to tick pay items upon deletion.
Go to the employee section and highlight the employee you want to reverse the leave pay-off.
Click on the Leave Entitlement tab and select the leave type you would like to reverse
Click the individual leave pay-off utility.
Select the payroll that contains the pay-off and input the hours to be reversed as a negative amount.
Once you press submit, go back to the payroll and recalculate the employee. Their entitlement will be reversed back to normal and no pay-off pay item will come up in the calculation.