The third estimated payment for 2019 is actually past due (it was due September 16th).
The last (4th) 2019 estimated payment is due January 15, 2020. You can use Form 1040-ES for that purpose.
See https://www.irs.gov/pub/irs-pdf/f1040es.pdf
You can also make estimated payments via the IRS Payments web site or EFTPS (links below).
EFTPS: https://www.eftps.com/eftps/
IRS Payments: https://www.irs.gov/payments
