I recieved a check already in 2020 How and where do I declare this on my filling?

You need to report the stimulus payments received on your tax return to calculate the Recovery Rebate Credit correctly. But the payments are not taxable.

1. Login to your account.
2. After entering all your information click "Federal Review" at the top of your screen. 
3. On the screen "Let's make sure you got the right stimulus amount" click "Continue".
4. Enter the amounts of first round and second round stimulus payments you received.