You amend 2020 to show that it was all returned. You will not need a 8915E in 2021 and 2022.
You should *wait* until your return has been processed and you receive your refund or conformation that any tax due has been paid. (If you file an amended return while you first return is being processed it can cause extended delays for both returns if two returns are in the system at the same time). In addition, if the IRS makes any change on your original return, you might end up having to amend the amendment – a sticky process that can take a year or more).
-- Then you can start the amend process.
It is suggested that it be mailed certified with return receipt (or other tracking service) to verify that the IRS receives it. That is the only proof of mailing that the IRS will accept.
-- Amended returns can be mailed or e-filed - allow 8-12 weeks - can take up to 16 weeks (4 months) for processing. (Because of current COVID delays expect 6 months or more.)
See this TurboTax FAQ for help with amending:
You can check the status of your amended return here but allow 3 weeks after filing for it to show up:
if you amend showing the distribution paid back,
Form 8915-E will drop off your 2020 tax return.
You should mention this in your Part III explanation.
If you e-Filed 1040 you get one e-File of 1040-X, prior to Oct 15, 2021. Use it wisely.
Basically, when you added the 1099-R before, you were asked what you did with the money, and you answered that you kept it, and that it was a COVID distribution. When you prepare your return, you will change your answer to "I returned it before the filing deadline" or "I returned it within 60 days."
What I don't know is whether Turbotax is programmed to include the choice "I returned it within 3 years". If that is a choice, pick it. But if Turbotax only allows the other two choices (which are the only allowable options for non-COVID distributions) it will be ok to use them because they will lead to the correct result.