Use current Instructions for 1040-X, they cover 2016, 17, 18, 19. The Form has boxes to check, i.e. 2019.
As Amended is a corrected redo of your 2019, only pages that change. I wrote "As Amended" on the top of each page so the IRS knows what that is.
So you file a 1040-X and a redo of 1040, for your 2019 year.
