To install Remote Control app click on the button bellow. You will also need a helper app installed on your computer, which you can find here. After installing the app you will have to unlock premium features in order to use this keypad. You can do it either by starting free trial, or by purchasing one time upgrade. Some of other premium app features also require an upgrade.
Find a file attached to the email or message you got, and tap on it (requires Remote Control app to be installed).
Select the app from the list (and if it doesn't appear in it - tap on More and find it there)
When the app opens it will present an alert asking you if you want to import the keypad, select Import and the keypad should appear in KEYS tab. Please note keypads are specific to operating system (macOS/Windows) and will appear only for appropriate computer types.