There should be a button on the CC's main page (on PC). Use it to show that your are unbound.
BTW: It's good to look at the CC members' list in "last day played" sorting. This shows the activity (last column), and be sure to check the owner's entry there. You'll want an active owner!
You might also want to contact the owner via his wall before applying to the CC. Might reveal more about the CC, and if he invites you, you're IN immediately after confirming.