If you are referring to the Indiana Post Filing Coupon payment voucher, you can find the form within your printed tax return. If you have not printed you tax return here are the instructions to print a tax return filed using TurboTax Online How
to print a copy of tax return after filing.
If you have already paid the Indiana Taxes due online you would not need to mail this payment voucher. It is only needed if you were mailing your payment.
Please reply below if this does not answer your question.