To map multiple boxes 12 and 14 items or if you need to report multiple different states' wages and tax, do the following.
Format your .csv file to have multiple columns for the same box. For example, if you need to report multiple box 12 items create separate columns for the separate box 12 items in your .csv file with the amounts reported for each employee in the appropriate column/row.
When you upload the .csv file into the Mapping Tool, all the column header names will appear on the left-hand side.