If TT's. Tier 3 says you can't e-file an 1040X for 2019, show them this Intuit Turbot Tax Tips article, updated for TY2020, which says you can. There's also links to downloads of Windows CD version, but I use Mac so haven't tried.
https://turbotax.intuit.com/tax-tips/amend-return/how-to-file-an-amended-return-with-the-irs/L6kO691...
