The most secure way to flash or recover firmware is through , the official desktop manager.
Unlike Samsung (Odin) or Xiaomi (Mi Flash), Huawei devices use proprietary flashing protocols. You can’t just copy a update.app file to an SD card anymore. For the P20 Lite, especially after the 2018 bootloader lockdown, you have two main options depending on your device’s status. huawei p20 lite firmware flash tool