Login to plesk control panel.
Then click on Files Tab.
You will see list of all files and folders of your home directory of this domain
Then click file or directory for which you want to set access permissions and click the arrow in the corresponding row. Then click Change Permissions in the drop-down menu.
Click on the appropriate User from left e.g. (Application pool group (IWPG_atozwebhost.com) )next adjust the permissions as required on the right. Then click OK