How do you amend your tax return for the 10,200 unemployment compensation break?

you don't.

IRS is in the process of fixing this for you.

If you filed before the program was updated for this situation then you do NOT need to amend the return ... the IRS will be fixing this issue on their end as they process your return so just sit tight. 

For taxpayers who already have filed and figured their 2020 tax based on the full amount of unemployment compensation, the IRS will determine the correct taxable amount of unemployment compensation. Any resulting overpayment of tax will be either refunded or applied to other taxes owed.

The agency will do these recalculations in two phases.

• First, taxpayers who are eligible to exclude up to $10,200.
   
• Second, those married filing jointly who are eligible to exclude up to $20,400, and others with more complex returns.

Phase one will begin in May.  A timeline for phase two has not yet been announced.

Taxpayers only need to file an amended return if the recalculations make them newly eligible for additional federal tax credits or deductions not already included on their original tax return.