The Edit Layer Class option is accessible only when a layer class is selected in the Layers to Plot region of the Gerber Setup dialog or ODB++ Setup dialog.
To access the Gerber Setup dialog, the UI.Unification.GerberDialog option in the Advanced Settings dialog must be disabled. The Advanced Settings dialog is accessed by clicking the Advanced button on the System – General page of the Preferences dialog. If any changes are made in the Advanced Settings dialog, the software must be restarted in order for the changes to take effect.
When the UI.Unification.GerberDialog option is enabled, the new Gerber Setup dialog is used for defining settings of Gerber files to be generated.
Layer Class Name - enter the desired layer class name or use the drop-down to select from the available layer names.