The payment deadline for a 2019 tax return was July 15, 2020. So if you did not pay yet, you are late. Send in your payment as soon as you can. The IRS will bill you for late penalties and interest based on how much you owe and when they receive your payment.
If you have federal tax due you can pay by mailing your payment with the 1040V voucher, (which has the address printed on it, having the payment taken out of a designated bank account, or you can pay directly on the IRS website.
You must pay your state tax due using the state’s preferred method of receiving payment. For most states that will be by making a payment to the state’s own tax website, or by mailing a check or money order.