Business Basics is not recommended for processing payroll, though if you do intend to use this software for payroll, and know the voluntary withholding rate, you can set up a tax code as follows;
Where the rate of 10% is replaced by your predefined voluntary witholding rate.
Then in your BASLink, link both W1 and W2 to the tax code PAY. Make sure that you test your set-up to see if it works and meets your needs.