Can't find the REFILE tab. Need to add a T4 to my 2018 Canadian Tax Return

The ReFile service for TurboTax Online users is not available until April, but you can do an adjustment online if you have a CRA My Account set up. 

CRA requires that you wait until you receive your Notice Of Assessment before you make any adjustments or ReFile that tax return. Here's instructions on how to go about that: https://turbotax.community.intuit.ca/replies/2647992