When I filed my taxes I hadn’t got my second stimulus check, then I got it, how will this effect my return now?

Once you sent your return to the IRS, it can't be changed. It's like putting a letter in the mailbox. You can't retrieve it.

 

If your return gets rejected, you'll be able to change your stimulus amount and submit the corrected return.

 

If your return gets accepted, you may need to amend your income tax return if the IRS includes the $600 stimulus in your refund. Wait for the IRS to process your return.

• NOTE: At this time, you're not able to  amend a 2020 income tax return. As of today, it's estimated that the IRS will finalize the 1040X form on 3/25/2021. However check the forms availability to see any updates to that date. 
• After you file your federal amended income tax return, you can check the status of your Form 1040-X, Amended U.S. Individual Income Tax Return using the Where's My Amended Return? online tool or by calling the toll-free telephone number 866-464-2050 three weeks after you file your amended return.

Note: Generally, Form 1040-X,  Amended U.S. Individual Income Tax Return, must be filed within three years of the date the original return was filed, or within two years of the date the tax was paid, whichever is later.

If the IRS includes the EIP2 in your refund, and does not make any changes,

you can just destroy or VOID that paper check.

WAIT