Quick Access Toolbar is a toolbar with a set of commands for you to quickly finish your work. If you want to add a separator between the commands to group them, please follow the steps below:
Step 1: Click the small triangle at the end of the Quick Access Toolbar;
Step 2: In the drop down list, click "More commands";
Step 3: In the new window, select "Separator" from the left box, then click "Add" button moving the separator to the location you want to group.
Step 4: Click "OK" at the bottom and you will see the separator in the Quick Access Toolbar.