Step 1: 

Tap on Download;

If you are an Android user

 

Step 2:

Open the Settings app on your iPhone/ iPad

Step 3:

Tap on Profile downloaded or;

Open settings < general < VPN & device management < downloaded profile.

Step 4:

Tap on Install the button in the top right corner.

Step 5: 

Enter your Passcode to confirm your installation.

Step 6:

Tap Install again

Step 7:

Go to your home screen and check for the "Premium YouTube" app