If you have 2 or more employers (for the same spouse) there is a max SS for box 4 and you can get the excess back. If you had more than one employer and the total of box 4 (only box 4 not box 6) on all your 2019 W2s for Social Security is more than $8,239.80 you get the excess back on your tax return on schedule 3 line 11. Which goes to 1040 line 18d.
That has nothing to do with W2 box 12.
