You will get the option for paying your federal tax due when you start step 2 of your filing process. Please view my screenshot below for reference.
If you have already e-filed then you will not get the option to set up an installment agreement. If that is the case, you can still file Form 9465 and request an installment agreement through the IRS. Please follow the Instructions for Form 9465 to apply for an installment agreement.
Other option: If you owe $50,000 or less, you may be able to avoid filing Form 9465 and establish an installment agreement online, even if you haven’t yet received a tax bill. Go to www.irs.gov/OPA to apply for an Online Payment Agreement
[Edited 04/08/2019 I 5:27 PM]
