If the IRS detects an error, most of the time they will send a letter informing you of the error, and proposing a tax assessment to correct the error. If you agree with the error and new tax computation, you just send a check to the address indicated in the letter. You don't have to file an amended return, because the IRS will adjust your return in their files to match their assessment. If you disagree that you made an error, or you agree that you made an error but disagree with the tax computation, you write back to the office explaining your disagreement.
