I received a statement of my Retirement Savings Plan Contribution Receipt in the mail and I don't know how to add the "Within First 60 Days of 2019" amount to my return

 

Seniors and students

To report any contributions you may have missed from the First 60 Days of 2019, CRA requires you to report them on your 2018 tax return. You'll need to make an adjustment or Refile the 2018 tax return. You can use "My Account" if you are set up to make an adjustment online, use the Refile service if you qualify, or print a paper copy and mail it to your tax centre.

https://turbotax.community.intuit.ca/replies/3639538