You did not understand it correctly. You don't necessarily get back the amount that was withheld from your unemployment checks. The amount you will get back has nothing to do with how much was withheld. What you get back is the tax on up to $10,200 of the unemployment benefits that you received, provided that your Adjusted Gross Income (AGI), not including unemployment, is less than $150,000. It's based on the tax that's calculated on your tax return, not the tax that was withheld.
The IRS will recalculate your tax return and send you the additional refund. It might take several months to get it. There is no way to track it or to find out in advance how much you will get back. For more details see the following IRS announcements.
IRS to recalculate taxes on unemployment benefits; refunds to start in May
IRS begins correcting tax returns for unemployment compensation income exclusion
IRS sending more than 2.8 million refunds to those who already paid taxes on 2020 unemployment compe...
