you need only to file 2020 Schedule 1 with line 7 showing your original UEC
and with line 8 showing the reduction as a negative number. (description : "UEC exclusion")
File 1040-X with your AGI ( Line 1) reduced by 10,200 or line 7 whichever is less
In explanation Part III explain IRS missed adjusting your return.
If the final tax (1040-X line 6 ) is wrong for whatever reason, IRS will recalculate the correct tax for you and send you the correct refund.
you can do all this by hand without tax software.
Get the blank 2020 forms in fillable PDF from IRS.gov.
As you know, a 2020 1040-X has to be mailed in anyway.
Note: Do not include your old 1040 nor your revised 1040 because the Form 1040-X reflects any changes there and becomes your new tax return.
@Nurex35
