If you filed an amended tax return, that would not only re-calculate your income tax based on the new exclusion, but it would also calculate a recovery rebate which would make up the difference between the stimulus payment you received and what you qualify for. At this time, the IRS is asking taxpayers affected by the new unemployment exclusion to wait. The IRS commissioner testified to Congress that it might be possible for the IRS to automatically re-calculate affected tax returns but they have not made a formal announcement of this. Until the IRS makes a formal announcement of how this situation should be handled, you should wait for additional instructions. At best, the IRS will figure it for you and send you the money, at worst, you will have to file an amended return to request the money which will take six months to process.
