If you've added the app and are having trouble finding it, go to page you added the app to. Under the cover photo and to the right of the word Photos, look for the word Welcome and click on it. If the app isn't on the first row of apps, click the More button to the right of the tabs. Here's a shortcut link to your pages.

If you're still having trouble accessing your tab, make sure you’re logged in as yourself and not as your page when editing page apps: From the top of your Page, click Edit Page then select Use Facebook as [your name].  Also, make sure to use the same facebook account you used when adding the app.