You didn't say when you filed the first amended return. Do not file a second amended return until you have received confirmation from the IRS that your first amended return has been completely processed.
There can be only one Form 1040-X in a tax file. You will make a copy of the file that contains the first amended return, and create the second Form 1040-X in the new file.
If you have not already done so, use Save As to save a copy of your first amended return with a different file name, so that you don't accidentally mess up the original file. You could add "Amend 2" to the file name, or something like that.
After doing the Save As you are working in the new copy. The new file name will be at the very top of the window. Make sure you have gone all the way through the amendment process for the first amended return. You have to click the Review tab and continue through the final review until you get to the screen that tells you to print and mail the amended return.
Now you have to tell TurboTax that you want to amend again. Click the Federal Taxes tab, then Other Tax Situations. On the Other Tax Situations screen, scroll down to Other Tax Forms and click the Update button for "Amend a return." It will ask you if you have already filed the first amended return. Select "Yes, it's been filed and accepted." Then select "I need to make additional changes to my 2020 return." The next screen tells you that it will clear your first amendment. Then proceed to make the changes for the second amended return. On the new Form 1040-X, column A will have the amounts from the first amended return.
If you have further questions, please say whether you are using 2020 TurboTax Premier in Windows or on a Mac.
