Ok ... if you choose the payment plan then no form 1040-V would have printed out to pay the bill in full and there are no such voucher for the "first payment" ... are you by chance looking at the 4 estimated payment forms 1040-ES ? Those are to pay your 2019 taxes in advance so you don't get behind again next year.
If you had set up a payment plan then you will have a form 9465 in your return PDF and the IRS will not review or approve that until after 4/15/19 and even then it takes 6 weeks or more to get a letter of acceptance or denial.
If you have not set up the installment payments then you can do so online directly at www.IRS.gov/payments/online-payment-agreement-application
