Hi pasang, 

By default, an employee's STP Payroll ID is identical to their employee ID (ie the system generated employee ID, as opposed to the External ID).

The employee's STP Payroll ID can be changed only if it meets the requirements of Scenario 2, Option 2 detailed in this transition article and the BMS ID of the employee's employing entity has changed. If there is no "Change" button in the employee's STP Payroll ID field then the BMS ID has not been changed and therefore there is no ability to change the employee's STP Payroll ID. 

Feel free to drop a comment below if you have any other questions.