You can switch on team auto-assignment in a course that has been published by following the steps below:
Note: All current and future members of your chosen team will be invited to the course
Go to Courses from the main menu, then click on Course Management
Search for the course you'd like to edit
Under the PARTICIPANTS area, click on Manage
Click on the Automatic assignments: Off button
Toggle to Yes then click the Selected teams only option
Search for the team or teams you'd like to add.
Note: You'll have to click to add each team individually
Click Save changes and you're good to go.