Why do you think you need to amend?
If you qualify for a rebate based on your income and number of dependents, Turbotax automatically adds it to your tax return. You have to take affirmative steps to remove it, by telling Turbotax if you already received the round 1 and round 2 stimulus checks. If you do not remove the rebate, it is added to your tax refund on line 30 of form 1040. It is part of your refund, it is not paid separately.
Check line 30 on the tax return you filed. Did it already claim a rebate? If not, then you may not qualify, and amending will make no difference. We would need more details to help you figure this out.
The round 3 stimulus is not part of your tax return, it will be paid separately.
