You must claim your T2202A tuition amounts the year
the T2202A was issued. In the same year, it must be used to offset any taxes
you have payable. If there is any amount left, it will be carried forward
throughout the years until it is used up. You can’t choose when to use your tuition,
though you can transfer some to a spouse, parent or grandparent in the year you
first claim it.
So to use your 2015, 2016, and 2017 T2202A tuition
amounts, you must adjust the returns for those years, starting with 2015. Then
you can add any amounts carried forward to your 2018 return, as well as your
2018 T2202A.
Here is how to claim tuition fees in TurboTax: https://turbotax.community.intuit.ca/replies/2647973
You can make changes after you have filed your tax
return through the CRA or through ReFILE:
https://turbotax.community.intuit.ca/replies/2647992
