To confirm you rolled the after-tax funds into your Roth 401(k)?
If yes , then all you need to do is enter your Form 1099-R and answer the follow-up questions:
- Click on "Search" on the top right and type “1099-R”
- Click on “Jump to 1099-R” and enter your 1099-R with code G
- On the "Did you move this money from a 401(k) to a Roth 401(k)?" screen answer "Yes"
- Continue through the questions.
Please see How do I amend my federal tax return for a prior year?
If the jump link doesn't work, select the "Wages & Income" tab and then scroll down to "IRA, 401(k), Pension Plan (1099-R)”.