HUAWEI P9 HARD RESET by Secret Code
How to Hard Reset HUAWEI L21 P9 Lite - Remove Screen Lock
How to Wipe All Data HUAWEI L21 P9 Lite - Factory Reset in HUAWEI
How to Reset HUAWEI P9 Lite - Reset Code / Format / Delet Data
Hard Reset will erase all of your data
All described operations you are doing at your own risk.