Samsung had said that the second Android 10 beta update for the Galaxy S9 and S9+ would be released this week, and the company has done just that. The second beta update is available now in India and should also be available in South Korea. It comes with software version G96*FXXU7ZSL2 and includes the security patch for the month of December.
At around 300 MB, the update isn't too big, but it seems to fix a few important issues, such as a data leak resulting from GPS usage, slow hotspot speeds, severe noise when using Bluetooth devices, device reboots when playing the Clash Royale game and when using a VPN, and slowdowns because of memory leaks. The new beta probably has some bugs as well, and there are likely going to be a few more beta updates before the stable Android 10 update arrives for the Galaxy S9 and Galaxy S9+.
You can download the second beta update over the air just like any other update. Open the Settings app on your phone, select Software update, then tap Download and install. As usual, it's advisable to backup all important data before you perform the update so you don't end up losing that data if you run into a device-breaking bug that forces you to do a factory reset.