Click on an assignment you've created to open the Heatmap, then go to the Skills.

In Skills, you'll see students listed on the left and skills on the top. This view offers more colors than the Heatmap and the percentage of the class that mastered the skills. To understand what each color means, click the information button.

If Practice mode is available to you:

Click on the skill. This will recommend a practice that targets that skill. A message will appear asking if you want to create the assignment. Click Recommend, and the assignment will be sent to students who scored below 50% on that skill.

The new assignment will appear in the Practice tab under Assignments.