You don't use the 2019 program. But if you used the Online version for 2018 you might have to wait for 2019 to be released to download the .tax2018 file to open in the 2018 Desktop program. Access to 2018 online returns might be limited right now as they transition over to 2019.
if you think you will owe on an amended return you can send in a payment to the IRS directly at
https://www.irs.gov/payments
