The link to the Beta was published in Samsung Members temporarily but was subsequently removed as it was not supposed to be released at this time. It shouldn't be too long until it's available again! Keep your eyes peeled on the Samsung Members app!
Whilst we're waiting there a few things we'd recommend you do. We recommend that you back up all of your data prior to downloading the Beta software. As this is not the official, final release of the software, unexpected data loss can occur in certain situations.
And make sure all apps are updated to the latest version as errors may incur due to compatibility issues. This should be done in the Play Store and the Galaxy Store. - Play Store > Main menu (Hamburger menu) > My Apps and Games > Update All - Galaxy Store > Menu (3 dots, top right) > My page > Updates > Update All.