Clear Cache Link on the Toolbar
One of the ways to clear cache is clicking on the link which exists on the admin toolbar. By default, only the admin users can see the clear cache button on the toolbar.
Although It only appears for admins as default, you can make it visible by user role. This feature allows you to show the clear cache button which exists on the admin toolbar based on user roles.
First you need to open the settings page of wp fastest cache. Then you need to click on the settings link as you can see in the picture below.
Then you can select the roles you want on the popup lighbox.
Hide Toolbar Link
If you want to hide toolbar link, you need to add the following line after <?php which exists on the top of wp-config.php file.