Click the next button.
Then you'll be presented with the 'Application Bundle Export Menu'.
The last option on this menu is 'Icon'. This is where you specify the .icns file to use as the dock icon.
Click the next button.
Then you'll be presented with the 'Application Bundle Export Menu'.
The last option on this menu is 'Icon'. This is where you specify the .icns file to use as the dock icon.