If you are an owner of the Mate 9 device, then you need to download a dedicated app from Huawei’s website to enroll into the beta program. Once the app downloaded, you need to sign-in with your Huawei ID and follow the instructions. And if you are eager to get into the program, then don’t wait as the company allows 250 users for the testing (at least for now).
And before you enroll, don’t forget that the beta program will have different numbers of bugs. You can report those bugs, the company will fix and will be able to roll out a polished version of Oreo. The beta program of Oreo will end on November 3, and there is no word about the time of official roll out but I’m guessing that it will happen before the end of this year.
So, download the app and be part of the beta program.