First, leave your current Club by selecting the ☰ icon while in Leagues and choosing "Leave Club". Once you leave, you will be shown a list of available Clubs. If the Club is invite-only you'll be able to apply to join. Keep in mind that applying will result in leaving your current Club, even if the application is eventually rejected.

To search for a specific Club you will need to leave your current Club, through the League menu in the upper right.

Leaving a Club will reset your season Stars to 0, even if you rejoin the same Club later in the Season.