If you put the authorization to withdraw your payment on the mailed form then the IRS will withdraw it after they process you tax return. They are in a huge backlog of work right now because of the covid 19 shutdown and it may be awhile. https://www.irs.gov/newsroom/irs-operations-during-covid-19-mission-critical-functions-continue
I would not pay electronically now because it is likely that you would be making a duplicate payment . Just wait for them to process your return.
Disclaimer: Not a tax professional. Information gathered from internet links. Anything dated in June 2019 was posted in prior years and is before the 2019 limits and changes.
