Did you efile? Was it Accepted? You either entered your bank account for the IRS to pull it out of your bank account or you send in a check.
How to pay a tax due
https://ttlc.intuit.com/community/tax-payments/help/how-can-i-pay-my-federal-taxes/00/26212
You can pay the IRS directly at
https://www.irs.gov/payments
Or here is a 1040V voucher slip
https://www.irs.gov/pub/irs-pdf/f1040v.pdf
