Form 1040X (PDF), Amended U.S. Individual Income Tax Return, is designed with three columns. Column A is used to show the figures from the original return. However, if you previously amended that return or it was changed by the IRS, enter the adjusted amounts. Column C is used to show the correct figures. The difference between the figures in Columns A and C is shown in Column B. On the back of the form you need to explain the specific changes being made on the return and the reason for each change. If the changes involve another schedule or form, attach it to Form 1040X (PDF). Be sure to enter the year of the return you are amending at the top of the form as required.

References:

• Form 1040X (PDF), Amended U.S. Individual Income Tax Return and Instructions
• Tax Topic 308, Amended returns

Source: www.irs.gov