Balance due returns are low man on the totem pole and will most likely not be processed until 7/15 or later. The online payment option on the IRS site should allow you to make a payment on the 2019 form 1040. If you cannot figure this out then you can mail in a payment instead ... send a 1040-V with the payment :
https://www.irs.gov/pub/irs-pdf/f1040v.pdf
