If you have not filed your 2018 tax return, you will need to file it first and CRA will apply any tuition credit amounts from 2017 that you have available. If you do not need to use all or any of the carry-forward amounts to reduce your 2018 tax payable, then CRA will update your available tuition carry-forward amounts.
If you have filed that 2018 tax return, CRA would have applied any amounts needed and will have a current carry-forward amount to use on your 2019 tax return.
You can check your online CRA My Account for the most up to date amounts, or call CRA General Enquiries 1-800-959-8281