This will guide you through the installation of the open-beta release of OOS.
- Go to Oneplus Software Center
- Select your phone and then click on the beta version button
- Download the open beta package
- Move the file to your internal storage (the folder where the downloads folder and the android folder is)
- Go to Settings -> System -> System upgrade -> Click the gear icon -> Select local upgrade -> select your open-beta package
- Install, reboot and enjoy!