[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.