The Beta version of Miui 9 is available now check your updater app if you are using beta rom else download the recovery rom and flash via updater app and the stable rom will be rolled out in a month or two
Hye, if you wants to roll back from miui 9 global beta to miui 8 global stable then the steps are mentioned below ;
Note : Please take a full backup of your device including all important data because all data gone a be wiped during this process.
Download the latest zip file of miui 188.8.131.52 from miui official website en.miui.com.
Then go to updater app and select the three dot option showing above.