Login to your website
On the home page Click on the Admin Panel --> Permission button.
Check the user name of at least one administrator.
Then - Go to the chosen page. You must be on the page where the permission is being given/restricted
Click on the Admin Panel --> Permission button
Users list will appear. Check the name of the editor for this page.
This will assign the user permission to this page and all other sub pages under this page.
Note:
Once one editor has been checked on a given page, no other editor will has access to edit that page unless their user name is also checked.
Once an editor has been checked on any page, they will no longer has access to any other page on the site.