See this TurboTax support FAQ for amending a tax return - https://ttlc.intuit.com/turbotax-support/en-us/help-article/tax-return/amend-change-correct-return-a...
Do not expect quick results from amending. It can take four to six months for the IRS to process an amended return--or longer.
You can watch for information here:
https://www.irs.gov/Filing/Individuals/Amended-Returns-(Form-1040-X)/Wheres-My-Amended-Return-1
Yes, you can file an amended return for tax year 2021 if you filed the return within a three-year period after filing the original. This is only if you received a refund in the original tax return.
If you owed taxes in the original preparation, you only have a two-year window in filing your amendment. For an example, today is March 14, 2024. You would have needed to file your original return later than March 14, 2022 to receive the credit, if you owed taxes on your 2021 tax return.
Based on what i just said, you can amend your 2020 tax return if you filed it later than 3/14/2021, if you received a refund for that year. If not, then no. If you owed taxes on your 2020 return, you would not be able to amend your 2020 return because it is outside the two-year window for filing if you owed tax on the 2020 tax return.
You can file your amendments electronically but it is best to use the original software you filed with. Otherwise, you would need to reconstruct the original return and then file an amendment based on the original tax data. This is challenging for many tax payers to do this. If you used Turbo Tax online or Software, here is how to file.
To amend your return using Turbo Tax Online.
To amend using the Desktop Software, go to:
If you used desktop in 2020 and/or 2021 you will need those tax year programs installed on your computer in order to prepare the amendments.
IRS Guide for Amending Returns