For those ONE PLUS 3T users who have a TWRP as there recovery, you can also have the BETA system in your unit. Don’t worry we will help you. 🙂
First things first! You take a back up of your current ROM in TWRP, so you can convert it back if you don’t want the BETA OS.
Follow the steps briefly so you will not have a problem in the future.
1. Download the latest BETA ROM at the site (about 1.4x GB in size)
2. Using file manager OR ES FILE EXPLORER, go to your download folder and cut the Zip file then paste it at the root of your storage. (No Folders) (Why we do this? So you can easily find the BETA ROM that you downloaded earlier.)
3. Turn OFF your device.
4. While the device is turned OFF, PRESS then HOLD the Power Button and Volume Down until boots into your recovery. (TWRP)
5. Inside the recovery menu, select Install via Zip.
(No wipe needed.)
6. Find the Beta Rom Zip file you’ve just downloaded and proceed with the installation.
7. After installing, DO NOT REBOOT YET (I SAID DO NOT REBOOT YET). Go back in the main menu, and go to WIPE selection (beside the INSTALL button), WIPE DALVIK Cache and Cache ONLY. (DO NOT WIPE DATA, SYSTEM and OTHER PARTITIONS so you won’t loose anything.)
8. After wiping, GO TO REBOOT SELECTION, but DON’T reboot yet to system, REBOOT to RECOVERY FIRST. Why? Just to ensure that you still have the TWRP Recovery.
9. After rebooting to recovery, you can now reboot to System.
10. Wait for about 10 to 15 minutes until the phone boots to the home screen.