You will need them after the reset.

This process, also known as a factory reset, restores the phone to its original manufacturer settings.

Since the P9 Lite runs on Android (likely Android 6.0 Marshmallow upgradable to 7.0 Nougat), it features . This is a security feature designed to prevent thieves from using a stolen phone. If you reset the phone, you will be required to sign in with the Google account previously synced on the device. If you do not know the email or password, you will be locked out. Make sure you know your login details!

: Release all buttons once the Huawei logo appears on the screen.