All tax documents must be entered during the year to which they were issued. You will want to enter last tax year's document by completing an amended 2016 tax return.
If you want to file an amended tax return after IRS accepted your tax return due to a mistake or a missing document, then you will want to wait until your original tax return is processed by the IRS. If you are receiving a refund, you will want to wait until the check is issued. Amended returns must be filed by mail.
