You can set/ change the Professional Tax to be calculated from one type to another (namely - Net Salary, Gross Salary, Earned Gross) by following the path.

Settings ---> HR Plus ---> Create Professional Tax Settings ---> (PT will be calculated on Gross Salary if you want to change Click here) will be shown ---> Click on Click Here button to change the type of PT Calculation ---> Select the Type of desired PT type

---> Click on Update.