2019 1040-X and its instruction caution to leave the dependent changes, lines 24-29 blank.
Neither is there a box to check stating, in an amended form, that someone can claim the taxpayer as a dependent.
My son-in-law failed to check the box to declare himself claimed as a dependent on our return.
As you describe in your message below, we could not efile. How can he amend his 2019? 1040-X appears to prohibit changes to dependent status for that year forward. Please help.
