To fix that, you have to open the SDK Manager, deselect the ‘Hide obsolete packages’ option on the bottom-right corner, and further, install the Android SDK Tools (obsolete) folder.

Have you ever wanted to create your own Android app? Whether you're a beginner or someone looking to enhance your mobile ...

You’ll find this in Android Studio if you navigate to Tools — Android — SDK Manager. You’ll see there are three tabs here for SDK Platforms, SDK Tools, and SDK Update Sites.

The Android R Preview SDK just appeared in the SDK Manager, meaning there's likely some new stuff to poke through. As you can see from the screenshot above, Android R revision 1 is now in the list.