TT's online instructions don't tell me anything useful. Apparently their tech writers don't have to test their advice by actually trying to apply it.
Did you do the original return in the Desktop program? You start by just opening your return as usual. Go up to File-Open. You need to have the .taxyyyy file on your computer.
Also you first need to check the filing status inside the program so it knows it was filed and accepted. Open your return and go up to the top black menu bar first item
File > Electronic Filing > Check Electronic Filing Status
Then save your return and close it. Close the program and reopen it.
If you don't see a button for Need to Amend a Filed Return? on your home screen then you can get to it here. Go to:
Federal Taxes -or- Personal (for H&B)
Other Tax Situations
last section, Other Tax Forms
Amend A Return - Click the Start or Update button
Be sure to save a copy of the original before doing anything. If you are using the online version, select Tax Home. Scroll to the bottom to Your tax returns and documents. Select the dropdown arrow. Select the year and amend option.
For the desktop version, see the instructions posted above.