From Joomla! Documentation

To 'add' a new administrator {{{module}}} module or 'edit' an existing administrator {{{module}}} module, navigate to the Module Manager, then switch to Administrator from Site:

  • Select Extensions  Module Manager
  • Click Administrator to switch list from site modules to a list of administrator modules

Click the 'New' button and click on administrator {{{module}}} in the modal popup window.

To 'Edit' an existing administrator {{{module}}} module, in the Module Manager click on the {{{module}}} Module's Title or click the {{{module}}} module's check box and then click the Edit button in the Toolbar.