User Registration not finished. Account created but not active - what next?

What can a new User do, if he didn't complete Registration?
That means, if he doesn't "Select a subscription" in Step 2. After Step 1, an E-Mail ist sent, but he can't login. Because his account is not yet active.

At this point, only Site-Support can help?
Or does the user has any possibility to activate his account by himself?

Thanks in advance,

PS: I'm using Buddypress + BP-Social + Membership.