There were several similar posts yesterday.
Now that 1.29.1.6316 is public, not beta, the update notification should sort itself out.
Plex Media Server checks in with plex.tv for hosts every few hours. If you wait it should eventually list the correct update.
You can force the issue by restarting PMS. It checks for available upgrades during the startup process.
If you want to update 1.29.1.6316 now, you can also download it from https://www.plex.tv/media-server-downloads/#plex-media-server.
