Hello @Pl1!
I'm sorry to be the bearer of bad news, but the deadline to add 1099 contractor history was 1/20/19. You'll probably need to amend the tax forms if they have the incorrect pay info.
For corrected 1099-MISC, you need to fill out the 1099-MISC with the correct amounts and check the Box on top that says Corrected.
Please note, if you decide to mail these forms, you need to mail the official forms found here, not their PDF version. The IRS also has additional information on filing the corrected forms here too.
Also you can use the Support Center Article How To Amend Duplicate Tax Filing.
