You do not need to mail anything in with your request for a Capital Loss Carryback. Although the CRA information does say "send in the form", with NetFiled returns nothing is actually "sent" in to CRA, nor is a T1ADJ required to adjust the prior year tax returns.
You can complete the information in TurboTax by using the "FIND" button, searching for "Losses" and complete the section that asks how much and which year you would like to "carryback" your losses to.
Here's some more information from TurboTax: https://turbotax.intuit.ca/tips/carrying-capital-losses-backward-or-forward-6249
