There are a few methods. There are only 10,000 slots available so the quicker you get setup the more likely you will be to get the update. It is worth noting that Samsung has the right to permanently kick you out of the program if they find out you used the backdoor to get in.
Only devices that meet the following requirements are eligible. You need a Snapdragon T-Mobile S8 or S8+, Snapdragon Sprint S8 or S8+, or a carrier unlocked Snapdragon S8 or S8+ purchased from Samsung.
The first method requires you to download the Samsung+ app, download and unzip this file click "start.bat", find the local IP address of your PC, Go to wi-fi settings on your S8 long press on current wi-fi network, tap "manage network settings, tap show advanced options, set your PC's IP address as the proxy server, change the port to 8888, finally open the Samsung+ app and receive the prompt for enrolling in the beta.
Method 2 is a bit more in depth. You can find both methods outlined in full at the link below.
via xda
