Not that you asked but you can't efile a 2020 1040-X.

Save and open the return you are amending and open the 1040-X  and input all the changes with the spouse W-2 and the amount of refund spouse received and it should reconcile on the form you may have some manual entries, since the 1040-X will calculate as Joint and not MFS.

You show what the spouse paid in by entering her/him W-2 form and any estimated taxes.