Similar to iOS 9 and 10, iOS 11 and 12 also places screen mirroring options in the control center on iPads, iPhones and iPods. 

Follow the steps below to mirror an iOS 11 or 12 iPad, iPhone or iPod:

1. Be sure your iOS device is on the same network as the computer that has Reflector 3 installed. 

2. Launch Reflector 3 on your computer. 

3. On your iOS device, swipe up from the bottom of the screen to open Control Center. If you're using an iPhone X, you'll need to swipe down from the top right corner of the phone to reveal Control Center.

4. Tap on the Screen Mirroring icon, and you should see a list of available devices. 

If you don't see the mirroring icon or any destinations in the list, refer to this help topic: I do not see my AirPlay icon.

5. Tap on your computer's name and your device will begin mirroring. 

Check out this video for more help: