If you've already filed with your rolled over distribution shown on Form 1040 line 4b as taxable, yes, you'll need to amend. Wait for your tax return to be processed, then amend using TurboTax by deleting the originally entered Form 1099-R, reentering it indicating that none of the distribution was RMD, indicating that you moved the money to another retirement account or back to the same account, then indicating the amount rolled over. TurboTax will then prepare Form 1040-X showing the change to your AGI, taxable income and tax. In the explanation you'll need to indicate that the change is because your originally filed tax return did not show the rollover. TurboTax will also update Form 1040 to exclude the rolled-over amount from line 4b and to include the word ROLLOVER next to this line, but you won't file that since the Form 1040-X with explanation takes its place.
