To amend prior state tax returns, each prior year will need to be downloaded from your tax history and then opened in TurboTax CD/Download for the applicable year. You may need to purchase access to this if it was not previously purchased.
Click this article for more details: How to amend (change or correct) a return you already filed
Access MI-1040 and Form 4884 Instructions for each prior year at Michigan Taxes: Treasury Forms Information. The Tax Area is Individual Income Tax.
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