Can I still make a payment after I filed an extension? I think I will owe more than the estimate on my extension and want to pay now rather than when I file my return.

[Anonymous]

it would seem you would need to mail in form 1040-V with payment.  there does not appear to be a method to pay online. 

[Opus 17]

You can make payments for any tax year at www.irs.gov/payments.  Make sure you select "2019" as the year and not 2020.  When you prepare your final return, you will need to add this extra payment manually on the Deductions and Credits page for "estimates and other taxes paid."