If you have a laptop or PC, download the Smart Switch app on both. Then open it, connect your phone with the original Samsung USB cable. The "downgrade" option will appear; click on it. This will take half an hour to an hour. Your device will downgrade from One UI 7 beta to the previous One UI 6.1. After the downgrade is complete, your phone will be completely reset. Then, go to System Update and check for updates. You will first get a patch update; finish it. Your phone will reboot. Then, check System Update again, and you will get the fresh One UI 7 stable version. (Make sure to back up your data before downgrading, because it will completely reset your device.)
Basically, this is the process for the beta to stable version. So don't panic when you see the old One UI 6.1, just relax and check for software updates.
