I’ve just spent tow frustrating hours going around the houses, trying to work out how to link my brand new Facebook I-frame app to my fan page. I’ve done this successfully before, but it was a while ago so this is a note to self. I’m constantly amazed at how despite such comprehensive documentation it can be so difficult to find things that are so fundamental to how a Facebook app works. So, in case it helps, to link a Facebook app to a fan page (other than the page you create for the app) you need to use this url:
Obviously replacing the capitalised details. The app ID is easy – found here in your app settings, the url as far as I can tell can be anything, just cut and paste your app url here and it will redirect you to it afterwards. When linking your Facebook app to the fan page, the link above will allow you to select which page you want to link to, submit this.
From here, go to your fan page > edit page > apps (in the left nav) and the new app should be listed, from which point you can choose to “link to this tab” and it will appear in your menu on the left.
The information for this was sourced from https://developers.facebook.com/docs/appsonfacebook/pagetabs/ hopefully it will help you with how to link a Facebook app to a fan page.