[Phone] How to downgrade OS version from Android 10 to Android 9 target version?
*Please be aware that after install this system image on a device, all the personal data will be erased, so please remember to back up your data first.
Step 1: Please download the downgrade image from ASUS officail website and then put the image file into the root directory of the MicroSD card.
Step 2: Insert MicroSD card and then power off the device.
Step 3: Long press with＂Power＂ key and ＂Volume Down＂ key together for at least 5 seconds to enter Recovery Mode (ZB632KL/ZB633KL(ZenFone Max M2) please go step 3-1, others go to Step 4).
Step 3-1: ZB632KL/ZB633KL(ZenFone Max M2) When android robot show up. press the power key + volume down key and then press volume up key.
Step 4: Please use＂Volume Down/Up＂ key to select menu on the screen. Choose＂Apply update from external storage＂, and then press ＂Power＂ key to enter the selection.
Step 5: Please use ＂Volume Down/Up＂key to select the downgrade file and then press ＂Power＂ key to make the selection, the process of downgrade will start.
Step 6: When the updating process is done, Choose＂Wipe data/factory reset＂and tap＂Yes＂ to perform the master clear.
Step 7: When the updating process is done, Choose＂Wipe cache partition＂and tap＂Yes＂ Select "" to clear the system cache
Step 8: Select＂Reboot system now＂ to complete the process.