I filed a 1040 return. Since then I received a Schedule K-1 from CPA for a company in which I am a partial owner. The form shows a loss so I need to amend my 2020 retur

[gilbartd1]

How do I do that?

[DoninGA]

An amended return, Form 1040-X, can only be printed and mailed to the IRS if the original tax return was not e-filed. The IRS will take up to 16 weeks or longer to process an amended tax return.

Before starting to amend the tax return, wait for the tax refund to be received or the taxes due to be paid and processed by the IRS.

See this TurboTax support FAQ on amending a tax return originally completed and filed using the 2020 TurboTax editions - https://ttlc.intuit.com/community/amending/help/how-do-i-amend-my-return/01/27439

[Critter-3]

Yes you should amend the return once the original return has been fully processed.  

To amend a return... 

Some quick ground rules:

1. Be sure the original return was filed and accepted.
2. DO NOT go back into the return or change anything before you start the amendment process.
3. Gather everything you need before you start.
4. Complete the entire amendment process before you log out.
5. Starting with 2020 tax returns you can E-File a 1040-X amended tax return.  All prior years must be printed and mailed.

 You can correct a return that you've already filed and had accepted.  Select the year that applies and use this guide to proceed.

Select your tax year for amending instructions:

• 2020
• 2019
• 2018
• 2017

For additional information please refer to  How to Amend