First, your account has to be at least 3-4 months old before you can lead a coven.
If you are planning to apply to lead an inactive coven, so far that I know applications are to be sent to Petrarca. But since he's mostly busy improving the site and its features, that he can't mail everyone back who mails him.
As it says on Petrarca's profile: "If I do not reply to your message within 1 day assume the answer is NO."
Of course, there are other options to leading a coven. You could make one that's offline, in your local area. You can find local covens/groups/organizations to join or lead here: