There are a couple things you need to do in order to get the app installed
1. You are also going to need an app called TestFlight. This is an app made by Apple that will let you install apps not from the App Store
2. If you already have a invite you can move on to step 3. If you need to request a new invite go here and fill out your email and password.
3. You should receive an email letting you know you have been invited to download the app. In that email press "View in TestFlight"
4. Casper Cop should now show up in TestFlight and give you the option to install. Updates will also appear here when available