The 1040x has not been updated yet on the IRS website. However, I have attached the link for the Schedule A instructions. You can see that the mortgage insurance premium has been approved again for 2019 and retroactively for 2018. They need to update the 1040x to add that line back in. It would fall under 8a. Once it's updated, it should then be updated on this site. No date has been given but hopefully in the next few weeks.
https://www.irs.gov/pub/irs-pdf/i1040sca.pdf
