You should first contact CRA directly and inquire if that Tuition Credit is indeed available. The CRA website can be confusing and generally, if you still have a Tuition Tax Credit available, it will show on your Notice of Assessment (NOA).
If you indeed have that credit available, CRA will automatically apply it for you in the first year you need it. If you verify that the credit has not been used and is still available, you can enter it in TurboTax following the instructions below. Just remember, the credit will only be applied if you have "tax payable". (meaning your taxable income on Line 260 is below $11,806).
https://turbotax.community.intuit.ca/replies/2647970