To add a device to your account, just sign in to your Elite account from the Hotspot Shield app on that device.
Learn how to sign in to your Hotspot Shield Elite account on the following platforms:
Max 5 devices per Elite account. You can have up to 5 devices linked to your Elite subscription/account. Once you've reached the 5 device limit, you will not be able to sign in from a new device, and you will get one of the following messages:
To add a new device, you need to remove a device from your Elite account. Learn how to remove a device from your account
In case you have a free account, you can try an Elite account for free here.