TurboTax Online makes this difficult.
It may be easiest to do it manually.
You must have a copy of the original tax return you want to update (or a transcript).
The simplest way is to prepare your correct tax return (using TurboTax for example, or other means) and print it.
Then lay the paper printouts of both returns (correct and original) side-by-side.
You now have all the information needed to prepare Form 1040-X by hand.
It's pretty straight-forward.
The blank form in fillable PDF format and its instructions are available at www.irs.gov.
Mail to the same address you would mail your original tax return.
Note : since your original return shows the old refund amount you have to combine your two refunds onto form 1040-X line 18 and do the arithmetic.
