Foodbook provide custom login page for manager admin. The default manager admin login page is /admin ( your-domain.com/admin ). Branch, kitchen manager and delivery boy should be login from here.
If you want to change the admin page you will do it easily. At first, create a page which you want as an admin page and go to settings options Page Settings -> Select Admin Page you will see the created page here now select and save. You could follow the screenshot for more clear :