For an RRSP contribution made before March 2, 2018, report it in the tax return for the tax year in which you made the contribution. You can make changes after you have filed your tax return through the CRA or through ReFILE: https://turbotax.community.intuit.ca/replies/2647992
Here is how to enter RRSP contributions in TurboTax: https://turbotax.community.intuit.ca/questions/1190212-how-do-i-enter-rrsp-contributions-in-turbotax
Unfortunately, RRSP contributions made from January 1, 2019, and March 1, 2019, cannot be added to the 2019 tax year return. RRSP contributions don't follow a calendar year for tax purposes. If you have RRSP contributions made in the first 60 days of the following tax year, those contributions are entered on the previous year's tax return. In essence, those RRSP contributions should have been included in last year's tax return; in this case in your 2018 tax year return.
Not to worry. You can still claim the contributions. You'll just need to file an adjustment, which you can find out about in this link: