To choose your favorite teams, go to the My Action tab and select the three dots (°°°) in the top right-hand corner. Select Settings, then click on Favorite Teams.
From here, you can add teams by clicking + Add Team or remove teams from your favorites by clicking the Edit option in the top right corner.
After you have edited your favorite teams, exit the page by clicking the arrow in the top left corner, and your teams will be saved.