This post contains a collection of Huawei P9 Plus stock rom / firmware for all variants. To know the exact firmware that is suitable for flashing on your Huawei P9 Plus, go to Settings > About. There you will get full device information that will help choose the right firmware.
Learn how to root Huawei P9 Plus without stress
How to flash Huawei P9 Plus stock firmware
and follow the instructions carefully to flash your Huawei P9 Plus stock firmware package.
Download credits: Somboons, xda