Navigate to your course, in the green navigation bar

1. Click on Assessments, a drop-down menu will appear
2. Click on Assignments

This action will open the Assignment Homepage. Choose the assignment to be assigned to groups, next to the name of the assignment.

3. Click on the downward arrow, a drop-down menu will appear
4. Click on Edit Assignment

This action will open the Edit Assignment Homepage, on the right side of the page,

1. Click on Submission & Completion

A menu will unfold, under Assignment Type,

2. Tick the box next to Group Assignment, the heading Group Category will appear
3. Click on the downward arrow, a drop-menu will appear with the different group categories
4. Select the group category of your choice

This assignment will be available for all the groups of the group category. 

At the bottom of the window,

5. Click on the blue button Save and Close to save the changes