Open the left-hand navigation menu, and under "My Info" select "Personal Tax Profile for (Your Name)".

For the question "Did you work in 2018?" select "Yes" and check off "I received tips or did casual labor and will not be getting a T4."

Then, again under the left-hand navigation menu, select the "Income" section. Press continue until you reach the page with the title "Other Employment Income Sources". 

This is where you should enter your combined income from the two places you work at that did not give you a T4A.