This process will erase all data on your phone. Back up everything before starting.
Use volume keys to navigate to and press Power to select. Select your downgrade file.
Copy the downloaded .zip file into the root directory (main folder) of a MicroSD card. Enter Recovery Mode: Power off the device.
You must use firmware that matches your device's SKU (e.g., WW for Worldwide, CN for China). Mixing SKUs will cause failure. Method 1: Using MicroSD Card (Recommended for ZE620KL)