Changing 1040 MFS to 1040X MFJ: When I enter a previously-paid tax amount from MY 1040 to my WIFE's 1040X (Sch 3, line 10) Tax Due does NOT reduce. What am I doing wrong?

Amended wife's 1040 to 1040X, transferred my separate income, expenses, deductions. Tried entering my previously-paid tax due to her 1040X (MFJ), but doesn't seem to reduce our tax liability.