Facebook has a somehow hidden way for addding applications as page tab. To do that, you need to enter the following URL into your browser and you will be prompted with the dialog to choose page which you want to add your application to.

https://www.facebook.com/dialog/pagetab?app_id=<your_app_id>&next=<your_app_url>

Of course, you should have configured your application to work as page tab in the Facebook Developer tool.