Setup a Custom App with a Custom Tab Icon using Woobox’s IFRAMEHOST
(This is after you have set a custom tab, if you need to add one then read Add a Custom Tab on Facebook page to learn more.)
Then continue to the page where you will find your App ID & App Secret where you can edit the custom icon and save changes.
Then Install your new App to your Pages
After entering your App ID and App Secret, you will be shown an Install Page Tabs button.
You install this once on your Facebook page. Click the Install Page Tabs button to install it onto your pages.
You can also manually install your apps by going to http://iframehost.com/util/installtab/YOURAPPID (Replace YOURAPPID with your actual App Id).