You have not mentioned what kind of 1099 you have from the past year. There are many different kinds of 1099's. But what you have to do to add income to a previous year's tax return is amend that return. (You were not thinking about just putting it on your next tax return, were you? Because you cannot do that
https://ttlc.intuit.com/questions/1894381-how-to-amend-change-or-correct-a-return-you-already-filed?...
A 1040X cannot be e-filed. It must be printed and mailed. It will take about 3-4 months for the IRS to process an amended return. It is a good idea to use a mailing service that will track it, like UPS or certified mail, so you will know it was received.
Wait about 3 weeks from mailing and you can check the status of your amended return:
https://www.irs.gov/Filing/Individuals/Amended-Returns-(Form-1040-X)/Wheres-My-Amended-Return-1
https://www.irs.gov/filing/individuals/amended-returns-form-1040-x/amended-return-frequently-asked-q...
https://ttlc.intuit.com/questions/1908543-do-i-need-to-amend
**Disclaimer: Every effort has been made to offer the most correct information possible. The poster disclaims any legal responsibility for the accuracy of the information that is contained in this post.**
