From the Clubs home page, tap the blue cogwheel icon next to your name and select the 'Leave Club' option to exit the Club you're currently in. You can also leave by tapping on the "Settings" gear icon in the top-right corner of the Clubs home screen.
 

 

 
Please note that leaving a Club in the midst of a Collection or Club Event will result in you not being able to Collect any rewards the Club you've left has earned. Additionally, any Collection Points you've earned while in that Club will remain there, and only new Collection Points you've earned will count towards the new Club joined.

 

Experiencing issues with leaving a Club? Check out this article HERE.