Do you need to generate a new Class Access Code replacing the older one? 

Follow these steps -

• Click the name of your class under the Classes label in the left navigation tray
• Click the Access Code Key symbol in the cover photo
• Click For Parents
• In the Parent Access Code screen, Click Reset
• Click Reset Code on the pop-up screen 

Note: A new Class Access Code is generated replacing the old one. The old access code cannot be used to join the class anymore. Only parents with the New Class Access Code can join the class.

Also View: 
Generating Class Access Code for my class