You can buy VRidge in desktop app after pairing your phone, at the "Play" screen. You will see button named "Unlock VRidge" there or you can go directly to this page.
GameWarp is an addon to VRidge which allows you to play non-VR games, like Witcher 3 or GTA V, in VR. You need to own VRidge in order to purchase GameWarp. If you don't own neither then you can buy both at discounted price. Visit THIS LINK to learn more.
Please try the free version before buying!