According to the Facebook developer documentation, you can link a Facebook app with a fan page by following these steps:
- Set your page category to “App Page” (found under “Brands & Products”).
- Set the title of the app and the page to the same title.
- Go to your App and select “App Details”
- Under “Contact Info” you will find “App Page”. There you will be able to create a new page or if all went well, select your page from a list.
That’s it! Very simple.