@jungdchinese,
Apologies for the confusion due to the setting description.
Actually, this setting is :
WP Admin area Access
Which means that for whom you want the access. Here you want to restrict the access for instructors only then select this setting
refer: http://prntscr.com/ll0gwj
Now admin area will e only accessible by administrators
I wanted to allow the instructor to access the Admin bar so that the instructor could issue the coupon. Now the instructor can access the admin bar. This problem is solved. Thank you.