You'll need to manually enter the amount in the W2 field.

 To do this you'll need to first delete the code in GST setup window and then enter the amount at W2 manually.

Deleting the code in the GST Setup window

1. Go to the menu: Other function > GST Setup > BAS fields.
2. Select PAYG Withholding and delete the code below W2: Amounts withheld from salary, wages and other payments > OK.
   

Entering the amount at W2 manually

1. Go to Reports > GST Reports > Business/Instalment Activity Statement.
2. Open the period: October - December 2018.
3. You can now enter the amount at W2 field in the PAYG withheld tab.

1. From the menu: Other Functions > Chart of Accounts > Maintain Chart, double click on the relevant account code.
2. In the Edit Account window > click the drop-down in GST Class and choose any code > OK.
   
   
3. Click Yes on the next window and then OK.

Now check the W2 amounts in PAYG withheld tab.

1. Go to Reports > GST Reports > Business/Instalment Activity Statement.
2. Open the period: October - December 2018.
3. Check the amount at W2 field in the PAYG withheld tab.