If you want root, and if you want to install a Custom ROM, you’d need to have your stock bootloader unlocked. In easy terms Unlocking the bootloader allows you to install custom Firmware on your Huawei Mate 9.
How to get a password to unlock the Bootloader on Huawei Mate 9.1. Check the IMEI of your Huawei Mate 9 by pressing *#06#
2. Go to Huawei warranty checker and type your IMEI
3. You will receive the required information, including Serial Number, Product Model and Product ID of your Huawei Mate 9
4. Go to EMUI Huawei
5. If you already have an account, please log in.
If you do not have an account, sign up to log in
6. Enter the required data in the appropriate fields
7. Enter the code from the picture to confirm that you are human
8. Press the Commit button
9. The bootloader password will be displayed