Hi! Welcome to the Samsung Members community!
Go to the Samsung Members app - Community - Beta.
If it doesn't show, it means, for whatever reason, your device can't right now. There are many factors: where did you buy it, what region is the device, is it region locked, is it locked to a network, etc. The only real answer is you can't force it; if it doesn't show, then it doesn't. I wouldn't be too worried about the beta; it's basically the same as UI 7. It's not an update; it's a beta and may come with issues.