There is no voucher for paying the deferred self-employment tax. Go to the following link on the IRS web site for instructions to pay the deferred tax.
How self-employed individuals and household employers repay deferred Social Security tax
The option to defer part of the self-employment tax is new for 2020. The IRS was late issuing the final forms and instructions, so all the tax software companies had to implement it in a rush. They didn't have time to plan it out thoroughly. So it has some rough edges. And it's only for 2020, so it's not worth any effort to improve how the software handles it.
