You can file an amended return. The normal statute of limitations for a tax return is three years. That means that you have three years from the due date of your return to amend your return. Inform the auditor if you are planning to amend a tax return under audit. Amending a return under audit usually results in a delayed audit process
Alternatively, you can provide the information to the auditor and also compute and give an amended tax return to that effect to the auditor to consider in the assessment of your taxes.
Let me know if you have any question.
Please note: This advice is provided with the understanding that all the relevant facts have been provided by you. Any change in facts might affect the advice given and hence may not be relied on in such cases. Nothing contained in this reply was intended or written to be used, can be used by any taxpayer, or may be relied upon or used by any taxpayer for the purposes of avoiding penalties that may be imposed on the taxpayer under the Internal Revenue Code of 1986, as amended.