How to report your stimulus check to the irs if you already filed your taxes?

[DoninGA]

It depends. 

Did you indicate on the tax return in the Federal Review section of the TurboTax program that you did not receive a stimulus payment and then after you filed the payment it was received?  IF so, the IRS will adjust the federal tax return that you filed and remove the Recovery Rebate Credit on the Form 1040 Line 30.  This will decrease your federal tax refund or increase the federal taxes owed.

If you indicated on your tax return in the Federal Review section that you have received all the stimulus payments you were eligible to receive then no further action is needed on your part.

[Critter-3]

Did you file the 2020 return saying you did not get the check and it just came in the mail ??? 

If so there is nothing you need to do ... the IRS will catch the error automatically but it could extend the processing time.