To switch Clubs, tap on another Club to see if it has an empty spot available. If it has vacancies, there will be a button that allows you to join. 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 Acorns to 0, even if you rejoin the same Club later in the Season.