You can only ReFile returns for the tax year 2018 or later. For older returns, you would have to use the Canada Revenue Agency (CRA)’s My Account service or send in a request by mail, using a completed Form T1-ADJ, T1 Adjustment Request.
You can log into the CRA’s My Account service on their website: My Account for Individuals
You can download the T1ADJ from this CRA webpage: T1-ADJ T1 Adjustment Request
For more information about changing your tax return, please see this TurboTax article: How to Change Your Tax Return AFTER You’ve Filed
As per the Canada Revenue Agency (CRA) ReFILE: Online adjustments for income tax and benefit returns ReFILE is an online service that lets individuals and EFILE service providers send online adjustments for income tax and benefit returns with certified NETFILE software and EFILE software. Individuals (NETFILE users) can use ReFILE to send adjustments for 2021, 2020, 2019 and 2018 returns.
To amend the other previous years please see the CRA page How to change a return?
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