Copied this of the OI website, thought it made more sense than what I first typed out.
Making a Virtual Line reservation
First things first: you’ll need to log in to your Universal Orlando account on the mobile app. Next, tap “Virtual Line” in the side navigation menu, followed by “Virtual Line Venues.” This will bring you to a list of attractions with Virtual Line reservations available. Select the attraction you’d like to ride and tap “Virtual Line Pass – Reserve.”
Next up, you’ll need to select how many people are in your travel party and choose your preferred return time. If there are multiple times available, the app will list a number of options so you can use the one that best works with your plan for the day. Once you’ve picked a time, simply tap “Reserve Virtual Line Pass.”
And it’s as easy as that! Once you’ve selected your time, your mobile app will show you a screen with your reservation details and a QR code. (We recommend you take a screenshot, although you’ll always be able to access this screen in the app later on if you need to!) Your next job is simple: have fun until your return time arrives.
Once it is time to ride, head to the attraction entrance with your QR code ready. A team member will scan it and grant you entry to the regular queue, which will generally be much shorter than usual.
OI pro tip: are all of the Virtual Line slots – like, say, for that pesky Hagrid – gone for the day? Fear not! Keep trying to refresh the app all throughout your time in the parks; it’s been our experience that, on busy days, this is necessary in order to secure a spot (and zip through the Forbidden Forest with Harry Potter’s good friend and sometimes-teacher).