I would start with the 2020 tax return
strictly speaking you're supposed to use the worksheets and attach worksheets to 8915-E/F.
On line 14 or 25 - depending on the type of account - you need the one third of your total repayment.
This makes the taxable amount zero.
You will use overrides. (If you're using TurboTax Online, that's not possible)
Ignoring the worksheets is the simplest way.
You have to explain on Form 1040-X what you did and why.
