Log into
https://webmail.inccrra.org, and click on the "App launcher" (1) in the top left of the screen.
Open the "All apps" screen by clicking on the "All apps" link (2)
Scroll down to the "Lists" app (3), click the 3-dot menu (4) and select "Pin to launcher" (5)
Now if you click the "App launcher" (1) you should see the "Lists" icon under "Apps"