The Extension Settings Module is actually a reports module. It will show you each extension on your system and whether that extension has Call Waiting, Do Not Disturb, Call Forwarding, VMX Locator, Follow-Me, and other features enabled or disabled.
This module may eventually be moved to the "Reports" tab and be renamed "Extension Settings Report."
To access the Extension Settings Module in FreePBX 2.10 and later, access the graphical user interface using a web browser. Click on the "Settings" pull down menu at the top and then select "Extension Settings".