For those who did not register for the Initial Access Program when it was opened, it is too late now, as Samsung no longer accepts testers.
For those who happen to have signed up, they are required to open a Galaxy App store and make sure all their Samsung apps are up to date. After that Bixby will change and ask you to set the voice feature by training your voice for it.
Bixby Voice, Siri's virtual assistant or Google Assistant on the phone and can talk to you, is scheduled to come in late May, but it seems too ambitious.
The launch was later reportedly delayed until the end of June.
Seeing the Beta version that is now being released for beta testers, it is expected that the public version will touch the Galaxy S8 later this month or around July.