If you have already signed up for the beta, you can click this link https://play.google.com/apps/testing/com.plexapp.android and enter back into the beta on Google Play, it will take a few hours and then a new update will be offered.
If you haven’t signed up for the Android beta before, you can go here to sign up: Join App Betas: Android (mobile), Android TV, Apple TV, iOS
Once your in, if you don’t want to wait for Google Play to offer the update, you can download the APK from here; Android (mobile) beta release notes - #224 by SamFromPlex
