If you have filed your tax return, you will have to wait until the IRS either Accepts or Rejects the return before you can amend. More information about amending a return can be found here: https://ttlc.intuit.com/replies/5624594
Once the return is open for amending then you can add this form under "Federal Taxes", then select "Wages and Income" and enter the form into the appropriate income section.